Encoding method and apparatus therefor, and decoding method and apparatus therefor

ABSTRACT

Provided is an image decoding method including determining a predicted quantization parameter of a current quantization group determined according to at least one of block split information and block size information, determining a difference quantization parameter of the current quantization group, determining a quantization parameter of the current quantization group, based on the predicted quantization parameter and the difference quantization parameter of the current quantization group, and inverse quantizing a current block included in the current quantization group, according to the quantization parameter of the current quantization group.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation application of U.S. patentapplication Ser. No. 16/913,583, filed on Jun. 26, 2020, which is acontinuation of International Application No. PCT/KR2019/000041, filedon Jan. 2, 2019, which claims priority from U.S. Provisional ApplicationNo. 62/612,770, filed Jan. 2, 2018 and U.S. Provisional Application No.62/628,410, filed on Feb. 9, 2018, the contents of all of which areincorporated herein by reference in their entirety.

TECHNICAL FIELD

The disclosure relates to an image encoding method and decoding method,and more particularly, to a method of efficiently encoding and decodinginformation about a motion vector.

BACKGROUND ART

When an image of high quality is encoded, a large amount of data isrequired However, because a bandwidth available for transmission of theimage data is limited, a data rate applied to transmission of the imagedata may be limited. Therefore, for efficient transmission of imagedata, there is a need for image data encoding and decoding methods withminimal deterioration in image quality and increased compression rates.

Image data may be compressed by removing spatial redundancies andtemporal redundancies between pixels. Because neighboring pixelsgenerally have common characteristics, encoding information of a dataunit consisting of pixels is transmitted to remove redundancies betweenthe neighboring pixels.

Pixel values of the pixels included in the data unit are not directlytransmitted but information about a method of obtaining the pixel valuesis transmitted. A prediction method, in which a pixel value that issimilar to an original value is predicted, is determined for each dataunit, and encoding information about the prediction method istransmitted from an encoder to a decoder. Because a prediction value isnot completely equal to the original value, residual data of adifference between the original value and the prediction value istransmitted from the encoder to the decoder.

When prediction is exact, a size of the encoding information forspecifying the prediction method is increased but a size of the residualdata is decreased. Therefore, the prediction method is determined, inconsideration of sizes of the encoding information and the residualdata. In particular, a data unit that is split from a picture hasvarious sizes, and in this regard, when a size of the data unit isincreased, there is an increased probability that accuracy of predictionis decreased, whereas the size of encoding information is decrease.Thus, a size of a block is determined according to characteristics of apicture.

The prediction method includes intra prediction and inter prediction.The intra prediction is a method of predicting pixels of a block frompixels adjacent to the block. The inter prediction is a method ofpredicting pixels by referring to pixels of a different picture referredto for a picture including the block. Therefore, spatial redundancy isremoved by the intra prediction, and temporal redundancy is removed bythe inter prediction.

When the number of prediction methods is increased, an amount ofencoding information for indicating the prediction method is increased.Thus, the amount of the encoding information may be decreased bypredicting, from a different block, the encoding information to beapplied to a block.

Because loss of image data is allowed to the extent that the human eyecannot recognize the loss, residual data may be lossy-compressedaccording to transformation and quantization processes, and by doing so,an amount of the residual data may be decreased.

DESCRIPTION OF EMBODIMENTS Technical Problem

Provided are an image encoding method and an image encoding apparatusfor determining a quantization parameter of a quantization group, basedon block split information and block size information. Provided are animage decoding method and an image decoding apparatus for determining aquantization parameter of a quantization group, based on block splitinformation and block size information.

Provided are an image encoding method and an image encoding apparatusfor matching a current block with a current quantization parameter unit,based on at least one of a position and a size of the current block.Provided are an image decoding method and an image decoding apparatusfor matching a current block with a current quantization parameter unit,based on at least one of a position and a size of the current block.

In addition, provided is a computer-readable recording medium havingrecorded thereon a program for executing, on a computer, the imageencoding method and the image decoding method according to an embodimentof the disclosure.

Solution to Problem

Provided is an image decoding method including: determining a predictedquantization parameter of a current quantization group determinedaccording to at least one of block split information and block sizeinformation; determining a difference quantization parameter of thecurrent quantization group; determining a quantization parameter of thecurrent quantization group, based on the predicted quantizationparameter and the difference quantization parameter of the currentquantization group; and inverse quantizing a current block included inthe current quantization group, according to the quantization parameterof the current quantization group.

Provided is an image decoding apparatus including a processor configuredto determine a predicted quantization parameter of a currentquantization group determined according to at least one of block splitinformation and block size information, determine a differencequantization parameter of the current quantization group, determine aquantization parameter of the current quantization group, based on thepredicted quantization parameter and the difference quantizationparameter of the current quantization group, and inverse quantize acurrent block included in the current quantization group, according tothe quantization parameter of the current quantization group.

Provided is an image decoding method including: matching a current blockto a current quantization parameter unit, based on at least one of aposition and a size of the current block; obtaining a predictedquantization parameter with respect to the current quantizationparameter unit; obtaining a difference quantization parameter withrespect to the current quantization parameter unit; determining aquantization parameter of the current quantization parameter unit, basedon the predicted quantization parameter and the difference quantizationparameter; and inverse quantizing the current block according to thequantization parameter of the current quantization parameter unit.

Provided is an image decoding apparatus including a processor configuredto match a current block to a current quantization parameter unit, basedon at least one of a position and a size of the current block, obtain apredicted quantization parameter with respect to the currentquantization parameter unit, obtain a difference quantization parameterwith respect to the current quantization parameter unit, determine aquantization parameter of the current quantization parameter unit, basedon the predicted quantization parameter and the difference quantizationparameter, and inverse quantize the current block according to thequantization parameter of the current quantization parameter unit.

Provided is a computer-readable recording medium having recorded thereona program for performing the image encoding method and the imagedecoding method.

The technical problems to be achieved by the disclosure are not limitedto the technical features described above, and other technical problemsmay be inferred from embodiments below.

Advantageous Effects of Disclosure

A quantization parameter of blocks is determined according to aquantization group or a quantization parameter unit, such thatinformation necessary for determining a quantization parameter may beefficiently compressed.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1A is a block diagram of an image encoding apparatus based oncoding units according to a tree structure, according to an embodimentof the disclosure.

FIG. 1B is a block diagram of an image decoding apparatus based oncoding units of a tree structure, according to an embodiment.

FIG. 2 illustrates a process by which the image decoding apparatusdetermines at least one coding unit by splitting a current coding unit,according to an embodiment.

FIG. 3 illustrates a process of determining at least one coding unit bysplitting a non-square coding unit, according to an embodiment

FIG. 4 illustrates a process of splitting a coding unit based on atleast one of block shape information and split shape information,according to an embodiment.

FIG. 5 illustrates a method of determining a preset coding unit fromamong an odd number of coding units, according to an embodiment.

FIG. 6 illustrates an order of processing a plurality of coding unitswhen the plurality of coding units are determined by splitting a currentcoding unit, according to an embodiment.

FIG. 7 illustrates a process of determining that a current coding unitis to be split into an odd number of coding units, when the coding unitsare not processable in a preset order, according to an embodiment.

FIG. 8 illustrates a process of determining at least one coding unit bysplitting a first coding unit, according to an embodiment.

FIG. 9 illustrates that a shape into which a second coding unit issplittable is restricted when the second coding unit having a non-squareshape, which is determined by splitting a first coding unit, satisfies apreset condition, according to an embodiment.

FIG. 10 illustrates a process of splitting a square coding unit whensplit shape information indicates that the square coding unit is not tobe split into four square coding units, according to an embodiment.

FIG. 11 illustrates that a processing order between a plurality ofcoding units may be changed depending on a process of splitting a codingunit, according to an embodiment.

FIG. 12 illustrates a process of determining a depth of a coding unit asa shape and size of the coding unit change, when the coding unit isrecursively split such that a plurality of coding units are determined,according to an embodiment.

FIG. 13 illustrates depths that are determinable based on shapes andsizes of coding units, and part indexes (PIDs) that are fordistinguishing the coding units, according to an embodiment.

FIG. 14 illustrates that a plurality of coding units are determinedbased on a plurality of preset data units included in a picture,according to an embodiment.

FIG. 15 illustrates a processing block serving as a unit for determininga determination order of reference coding units included in a picture,according to an embodiment.

FIG. 16 illustrates an image decoding apparatus for determining aquantization parameter of a block and decoding residual data of theblock according to the determined quantization parameter.

FIGS. 17A to 17D are diagrams of embodiments in which a quantizationgroup is determined according to the number of quadtree splitting times.

FIGS. 18A to 18C illustrate an embodiment of a method of determining aquantization group in a largest coding block to which non quadtree splitis applied.

FIG. 19 illustrates a syntax structure about a method of decoding adifference quantization parameter included in a bitstream when quadtreesplit and non-quadtree split are all allowed.

FIG. 20 illustrates an image decoding method of determining aquantization parameter of a block according to a quantization group, anddecoding residual data of a block according to the determinedquantization parameter.

FIG. 21 illustrates an embodiment of a quantization parameter unitstructure and a coding block tree structure.

FIGS. 22A and 22B illustrate a method of determining a quantizationparameter unit corresponding to a current block.

FIGS. 23A and 23B illustrate a correlation between a block and aquantization parameter unit.

FIG. 24 illustrates an image decoding method of determining aquantization parameter of a block according to a quantization parameterunit, and decoding residual data of the block according to thedetermined quantization parameter.

BEST MODE

Provided is an image decoding method including: determining a predictedquantization parameter of a current quantization group determinedaccording to at least one of block split information and block sizeinformation; determining a difference quantization parameter of thecurrent quantization group; determining a quantization parameter of thecurrent quantization group, based on the predicted quantizationparameter and the difference quantization parameter of the currentquantization group; and inverse quantizing a current block included inthe current quantization group, according to the quantization parameterof the current quantization group. Also, provided is an image decodingapparatus including a process for performing the image decoding method.

Provided is an image decoding method including: matching a current blockto a current quantization parameter unit, based on at least one of aposition and a size of the current block; obtaining a predictedquantization parameter with respect to the current quantizationparameter unit; obtaining a difference quantization parameter withrespect to the current quantization parameter unit; determining aquantization parameter of the current quantization parameter unit, basedon the predicted quantization parameter and the difference quantizationparameter; and inverse quantizing the current block according to thequantization parameter of the current quantization parameter unit. Also,provided is an image decoding apparatus including a process forperforming the image decoding method.

Mode of Disclosure

Advantages and features of embodiments and methods of accomplishing thesame may be understood more readily by reference to the embodiments andthe accompanying drawings. In this regard, the disclosure may havedifferent forms and should not be construed as being limited to theembodiments set forth herein. Rather, these embodiments are provided sothat this disclosure will be thorough and complete and will fully conveythe concept of the disclosure to one of ordinary skill in the art.

The terms used in the specification will be briefly defined, and theembodiments will be described in detail.

All terms including descriptive or technical terms which are used in thespecification should be construed as having meanings that are obvious toone of ordinary skill in the art. However, the terms may have differentmeanings according to the intention of one of ordinary skill in the art,precedent cases, or the appearance of new technologies. Also, some termsmay be arbitrarily selected by the applicant, and in this case, themeaning of the selected terms will be described in detail in thedetailed description of the disclosure. Therefore, the terms used in thedisclosure should not be interpreted based on only their names but haveto be defined based on the meaning of the terms together with thedescriptions throughout the specification.

In the following specification, the singular forms include plural formsunless the context clearly indicates otherwise.

When a part “includes” or “comprises” an element, unless there is aparticular description contrary thereto, the part may further includeother elements, not excluding the other elements. In the followingdescriptions, terms such as “unit” indicate software or a hardwarecomponent such as a field programmable gate array (FPGA) or anapplication specific semiconductor (ASIC), and the “unit” performscertain functions. However, the “unit” is not limited to software orhardware. The “unit” may be formed so as to be in an addressable storagemedium, or may be formed so as to operate one or more processors. Thus,for example, the term “unit” may refer to components such as softwarecomponents, object-oriented software components, class components, andtask components, and may include processes, functions, attributes,procedures, subroutines, segments of program code, drivers, firmware,micro codes, circuits, data, a database, data structures, tables,arrays, or variables. A function provided by the components and “units”may be associated with the smaller number of components and “units”, ormay be divided into additional components and “units”.

The term “current block” indicates one of a current coding unit to beencoded or decoded, a prediction unit, and a transform unit. Forconvenience of description, when it is required to distinguish betweenother types of blocks such as a prediction unit, a transform unit, orthe like, the terms “current coding block”, “current prediction block”,“current transform block” may be used. Also, a “lower block” denotes adata unit split from a “current block”. An “upper block” denotes a dataunit including a “current block”.

Hereinafter, a “sample” denotes data assigned to a sampling position ofan image, i.e., data to be processed. For example, pixel values of animage in a spatial domain and transform coefficients on a transformdomain may be samples. A unit including at least one such sample may bedefined as a block.

Hereinafter, the disclosure will now be described more fully withreference to the accompanying drawings for one of ordinary skill in theart to be able to perform the embodiments without any difficulty. Inaddition, portions irrelevant to the description will be omitted in thedrawings for a clear description of the disclosure.

FIG. 1A is a block diagram of an image encoding apparatus 100 based oncoding units according to a tree structure, according to an embodimentof the disclosure.

The image encoding apparatus 100 may include an encoder 110 and abitstream generator 120.

The encoder 110 splits a picture or a slice included in the picture intoa plurality of largest coding units according to sizes of the largestcoding units. The largest coding units may be data units having a sizeof 32×32, 64×64, 128×128, 256×256 or the like, and may each be a squaredata unit having a width and length in powers of 2. The encoder 110 mayprovide the bitstream generator 120 with largest coding unit sizeinformation indicating a size of a largest coding unit. The bitstreamgenerator 120 may add the largest coding unit size information to abitstream.

The encoder 110 determines coding units by splitting the largest codingunit. Whether to split a coding unit is determined according to whetherit is efficient to split the coding unit by rate-distortionoptimization. In addition, split information indicating whether thecoding unit is split may be generated. The split information may berepresented in the form of a flag.

A coding unit may be split in various ways. For example, a square codingunit may be split into four square coding units, the width and height ofwhich are half those of the square coding unit. The square coding unitmay be split into two rectangular coding units having a width half thatof the square coding unit. The square coding unit may be split into tworectangular coding units having a height half that of the square codingunit. The square coding unit may be split into three coding units bysplitting the width or height thereof into a ratio of 1:2:1.

A rectangular coding unit having a width twice a height thereof may besplit into two square coding units. A rectangular coding unit having awidth twice a height thereof may be split into two square coding unitshaving a width four times a height thereof. A rectangular coding unithaving a width twice a height thereof may be split into two rectangularcoding units and one square coding unit by splitting the width of therectangular coding unit into a ratio of 1:2:1.

Equally, a rectangular coding unit having a height twice a width thereofmay be split into two square coding units. A rectangular coding unithaving a height twice a width thereof may be split into two rectangularcoding units having a height four times a width thereof. Equally arectangular coding unit having a height twice a width thereof may besplit into two rectangular coding units and one square coding unit bysplitting the height of the rectangular coding unit into a ratio of1:2:1.

When two or more splitting methods are applicable to the image encodingapparatus 100, information about a splitting method applicable to acoding unit among the splitting methods applicable to the image encodingapparatus 100 may be determined for each picture. Thus, only specificsplitting methods may be determined to be used for each picture. Whenthe image encoding apparatus 100 employs only one splitting method,information about a splitting method applicable to a coding unit is notadditionally determined.

A coding unit of a particular size may be split by using a particularsplitting method. For example, when a size of the coding unit is256×265, the coding unit may be set to be split into only four squarecoding units whose width and height are half the coding unit.

When split information of a coding unit indicates that the coding unitis to be split, split shape information indicating a splitting method ofthe coding unit may be generated. When there is only one splittingmethod applicable to a picture to which the coding unit belongs, thesplit shape information may not be generated. When a splitting method isadaptively determined based on encoding information about the vicinityof the coding unit, the split shape information may not be generated.

As described above, image data of a current picture is split intolargest coding units according to a maximum size of the coding unit. Thelargest coding unit may include coding units that are hierarchicallysplit from a largest coding unit. A shape and a position of a lowercoding unit may be determined based on a split shape of an upper codingunit. A minimum size of a coding unit which limits split of a codingunit may be preset.

The encoder 110 compares coding efficiency when the coding unit ishierarchically split from coding efficiency when the coding unit is notsplit. Then, the encoder 110 determines whether to split the codingunit, according to a result of the comparison. When it is determinedthat it is more efficient to split the coding unit, the encoder 110hierarchically splits the coding unit. The coding unit is not split whenthe result of comparison reveals that it is efficient not to split thecoding unit. Whether to split the coding unit may be determinedindependently of whether to split other coding units adjacent to thecoding unit.

A coding unit that is split last may be predicted due to interprediction or inter prediction. Intra prediction is a method ofpredicting samples of a prediction unit by using reference samplesaround the prediction unit. Inter prediction is a method of predictingsamples of a prediction unit by obtaining a reference sample from areference picture referenced for a current picture.

For intra prediction, the encoder 110 may select a most efficient intraprediction method by applying a plurality of intra prediction methods toa prediction unit. Intra prediction methods include a DC mode, a planarmode, a directional mode such as a vertical mode and a horizontal mode,or the like.

Intra prediction may be performed for each prediction unit when areconstructed sample around a coding unit is used as a reference sample.However, when a reconstructed sample in the coding unit is used as areference sample, a reference sample in the coding unit should be firstreconstructed and thus a prediction order of a prediction unit may besubordinate to a transformation order of a transform unit. Therefore,when the reconstructed sample in the coding unit is used as a referencesample, only an intra prediction method for transform unitscorresponding to the prediction unit is determined for the predictionunit and intra prediction may be performed substantially for eachtransform unit.

The encoder 110 may select a most efficient inter prediction method bydetermining an optimal motion vector and a reference picture. For interprediction, the encoder 110 may determine a plurality of motion vectorcandidates among coding units spatially and temporally neighboring to acurrent coding unit, and determine a most efficient motion vector as amotion vector among the plurality of motion vector candidates. Equally,a plurality of reference picture candidates may be determined among thecoding units spatially and temporally neighboring to the current codingunit, and a most efficient reference picture may be determined among theplurality of reference picture candidates. In an embodiment, a referencepicture may be determined from a reference picture list determined inadvance for a current picture. In an embodiment, for accurateprediction, a most efficient motion vector among a plurality of motionvector candidates may be determined as a predicted motion vector and amotion vector may be determined by correcting the predicted motionvector. Inter prediction may be parallel performed for each predictionunit included in a coding unit.

The encoder 110 may reconstruct a coding unit by obtaining onlyinformation representing a motion vector and a reference pictureaccording to a skip mode. According to the skip mode, all encodinginformation including a residual signal is omitted except for theinformation representing the motion vector and the reference picture.Because the residual signal is omitted, the skip mode is applicable whenthe accuracy of prediction is very high.

The partition mode to be used may be limited according to a predictionmethod for a prediction unit. For example, only a partition mode forprediction units having sizes of 2N×2N and N×N may be applied to intraprediction, while a partition mode for prediction units having sizes of2N×2N, 2N×N, N×2N and N×N may be applied to inter prediction. Inaddition, only a partition mode for a prediction unit having a size of2N×2N may be applied to a skip mode of inter prediction. A partitionmode allowed for each prediction method in the image encoding apparatus100 may be changed according to coding efficiency.

The image encoding apparatus 100 may perform transformation based on acoding unit. The image encoding apparatus 100 may transform residualdata, which are the differences between original values of pixelsincluded in a coding unit and prediction values thereof, by a presetprocess. For example, the image encoding apparatus 100 may perform lossycompression on the residual data by quantization and discrete cosinetransform (DCT)/discrete sine transform (DST) transformation.Alternatively, the image encoding apparatus 100 may perform losslesscompression on the residual data without quantization.

In conclusion, the encoder 110 determines the most efficient predictionmethod for a current coding unit from among a plurality of intraprediction methods and inter prediction methods. Then, the encoder 110determines a prediction method of the current coding unit, based oncoding efficiency according to a result of the prediction. Equally, theencoder 110 may determine a transformation method based on codingefficiency according to a result of the transformation. Based on themost efficient prediction method and transformation method determiningscheme with respect to a coding unit, coding efficiency of the codingunit is finally determined. The encoder 110 determines a hierarchicalstructure of a largest coding unit according to coding efficiency of afinally-split coding unit.

The encoder 110 may measure coding efficiency of coding units,prediction efficiency of prediction methods, etc. by using a Lagrangianmultiplier-based rate-distortion optimization technique.

The encoder 110 may generate split information indicating whether acoding unit is split, based on the determined hierarchical structure ofthe largest coding unit. The encoder 110 may generate partition modeinformation for determining a prediction unit and transform unit splitinformation for determining a transform unit with respect to a splitcoding unit. When there are two or more splitting methods of a codingunit, the encoder 110 may generate split shape information indicating asplitting method, together with split information. Then, the encoder 110may generate information about a prediction method and a transformationmethod used for a prediction unit and a transform unit.

The bitstream generator 120 may output information generated by theencoder 110 in the form of a bitstream based on a hierarchical structureof a largest coding unit.

A method of determining a coding unit, a prediction unit, and atransform unit according to a tree structure of a largest coding unitaccording to an embodiment will be described in detail with reference toFIGS. 3 to 12 below.

FIG. 1B is a block diagram of an image decoding apparatus 150 based oncoding units of a tree structure, according to an embodiment.

The image decoding apparatus 150 includes a receiver 160 and a decoder170.

Various terms such as “coding unit”, “prediction unit”, “transformunit”, and various “split information” related to a decoding operationof the image decoding apparatus 150 according to an embodiment are asdescribed above with reference to FIG. 1 and the image encodingapparatus 100. In addition, the image decoding apparatus 150 isconfigured to restore image data and thus various encoding methods usedin the image encoding apparatus 100 are applicable to the image decodingapparatus 150.

The receiver 160 receives and parses a bitstream of an encoded image.The receiver 160 extracts information necessary to decode each largestcoding unit from the parsed bitstream and provides the information tothe decoder 170. The receiver 160 may extract information about amaximum size of a coding unit of a current picture from a header, asequence parameter set, or a picture parameter set for the currentpicture.

The receiver 160 extracts, from the parsed bitstream, split informationof coding units of a tree structure for each largest coding unit. Theextracted split information is output to the decoder 170. The decoder170 may determine a tree structure of a largest coding unit by splittingthe largest coding unit according to the extracted split information.

The split information extracted by the decoder 170 is split informationof a tree structure determined by the image encoding apparatus 100 togenerate a minimum encoding error. Therefore, the image decodingapparatus 150 may reconstruct an image by decoding data according to anencoding method that generates the minimum encoding error.

The decoder 170 may extract split information about a data unit such asa prediction unit and a transform unit included in a coding unit. Forexample, the decoder 170 may extract information about a most efficientpartition mode for a prediction unit. The decoder 170 may extracttransform partition information of a tree structure that is mostefficient in a transform unit.

The decoder 170 may obtain information about a prediction method that ismost efficient in prediction units split from a coding unit. The decoder170 may obtain information about a transformation method that is mostefficient in transform units split from a coding unit.

The decoder 170 extracts information from the bitstream according to amethod of configuring the bitstream by the bitstream generator 120 ofthe image encoding apparatus 100.

The decoder 170 may split a largest coding unit into coding units of amost efficient tree structure, based on the split information. Thedecoder 170 may split a coding unit into prediction units according toinformation about a partition mode. The decoder 170 may split the codingunit into transform units according to the transform split information.

The decoder 170 may predict a prediction unit according to informationabout a prediction method. The decoder 170 may perform inversequantization and inverse transformation on residual data correspondingto the difference between an original value and a prediction value of apixel, based on information about a method of transforming a transformunit. In addition, the decoder 170 may reconstruct pixels of a codingunit according to a result of predicting a prediction unit and a resultof transforming a transform unit.

FIG. 2 illustrates a process by which the image decoding apparatus 150determines at least one coding unit by splitting a current coding unit,according to an embodiment.

According to an embodiment, the image decoding apparatus 150 maydetermine a shape of a coding unit by using block shape information andmay determine a shape into which the coding unit is to be split by usingsplit shape information. That is, a method of splitting a coding unit,the method being indicated by the split type information, may bedetermined based on a block shape indicated by the block shapeinformation employed by the image decoding apparatus 150.

According to an embodiment, the image decoding apparatus 150 may use theblock shape information indicating that the current coding unit has asquare shape. For example, the image decoding apparatus 150 maydetermine whether not to split a square coding unit, whether tovertically split the square coding unit, whether to horizontally splitthe square coding unit, or whether to split the square coding unit intofour coding units, based on the split shape information. Referring toFIG. 2, when the block shape information of a current coding unit 200indicates a square shape, the decoder 180 may determine that a codingunit 210 a having the same size as the current coding unit 200 is notsplit, based on the split shape information indicating not to performsplitting, or may determine coding units 210 b, 210 c, or 210 d splitbased on the split shape information indicating a preset splittingmethod.

Referring to FIG. 2, according to an embodiment, the image decodingapparatus 150 may determine two coding units 210 b obtained by splittingthe current coding unit 200 in a vertical direction, based on the splitshape information indicating to perform splitting in a verticaldirection. The image decoding apparatus 150 may determine two codingunits 210 c obtained by splitting the current coding unit 200 in ahorizontal direction, based on the split shape information indicating toperform splitting in a horizontal direction. The image decodingapparatus 150 may determine four coding units 210 d obtained bysplitting the current coding unit 200 in vertical and horizontaldirections, based on the split shape information indicating to performsplitting in vertical and horizontal directions. However, splittingmethods of the square coding unit are not limited to the above-describedmethods, and the split shape information may indicate various methods.Preset split shapes by which the square coding unit is to be split willbe described in detail below in relation to various embodiments.

FIG. 3 illustrates a process, performed by the image decoding apparatus150, of determining at least one coding unit by splitting a non-squarecoding unit, according to an embodiment.

According to an embodiment, the image decoding apparatus 150 may useblock shape information indicating that a current coding unit has anon-square shape. The image decoding apparatus 150 may determine whethernot to split the non-square current coding unit or whether to split thenon-square current coding unit by using a preset splitting method, basedon split shape information. Referring to FIG. 3, when the block shapeinformation of a current coding unit 300 or 350 indicates a non-squareshape, the image decoding apparatus 150 may determine that a coding unit310 or 360 having the same size as the current coding unit 300 or 350 isnot split, based on the split shape information indicating not toperform splitting, or determine coding units 320 a and 320 b, 330 a to330 c, 370 a and 370 b, or 380 a to 380 c split based on the split shapeinformation indicating a preset splitting method. Preset splittingmethods of splitting a non-square coding unit will be described indetail below in relation to various embodiments.

According to an embodiment, the image decoding apparatus 150 maydetermine a splitting method of a coding unit by using the split shapeinformation and, in this case, the split shape information may indicatethe number of one or more coding units generated by splitting a codingunit. Referring to FIG. 3, when the split shape information indicates tosplit the current coding unit 300 or 350 into two coding units, theimage decoding apparatus 150 may determine two coding units 320 a and320 b, or 370 a and 370 b included in the current coding unit 300 or350, by splitting the current coding unit 300 or 350 based on the splitshape information.

According to an embodiment, when the image decoding apparatus 150 splitsthe non-square current coding unit 300 or 350 based on the split shapeinformation, the current coding unit may be split in consideration of aposition of a long side of the non-square current coding unit 300 or350. For example, the image decoding apparatus 150 may determine aplurality of coding units by dividing a long side of the current codingunit 300 or 350, in consideration of the shape of the current codingunit 300 or 350.

According to an embodiment, when the split shape information indicatesto split a coding unit into an odd number of blocks, the image decodingapparatus 150 may determine an odd number of coding units included inthe current coding unit 300 or 350. For example, when the split shapeinformation indicates to split the current coding unit 300 or 350 intothree coding units, the image decoding apparatus 150 may split thecurrent coding unit 300 or 350 into three coding units 330 a, 330 b, and330 c, or 380 a, 380 b, and 380 c. According to an embodiment, the imagedecoding apparatus 150 may determine an odd number of coding unitsincluded in the current coding unit 300 or 350, and not all thedetermined coding units may have the same size. For example, a presetcoding unit 330 b or 380 b from among the determined odd number ofcoding units 330 a, 330 b, and 330 c, or 380 a, 380 b, and 380 c mayhave a size different from the size of the other coding units 330 a and330 c, or 380 a and 380 c. That is, coding units which may be determinedby splitting the current coding unit 300 or 350 may have multiple sizesand, in some cases, all of the odd number of coding units 330 a, 330 b,and 330 c, or 380 a, 380 b, and 380 c may have different sizes.

According to an embodiment, when the split shape information indicatesto split a coding unit into an odd number of blocks, the image decodingapparatus 150 may determine an odd number of coding units included inthe current coding unit 300 or 350, and may put a preset restriction onat least one coding unit from among the odd number of coding unitsgenerated by splitting the current coding unit 300 or 350. Referring toFIG. 3, the image decoding apparatus 150 may allow a decoding method ofthe coding unit 330 b or 380 b to be different from that of the othercoding units 330 a and 330 c, or 380 a and 380 c, wherein the codingunit 330 b or 380 b is at a center position from among the three codingunits 330 a, 330 b, and 330 c, or 380 a, 380 b, and 380 c generated bysplitting the current coding unit 300 or 350. For example, the imagedecoding apparatus 150 may restrict the coding unit 330 b or 380 b atthe center position to be no longer split or to be split only the presetnumber of times, unlike the other coding units 330 a and 330 c, or 380 aand 380 c.

FIG. 4 illustrates a process, performed by the image decoding apparatus150, of splitting a coding unit based on at least one of block shapeinformation and split shape information, according to an embodiment.

According to an embodiment, the image decoding apparatus 150 maydetermine to split or not to split a square first coding unit 400 intocoding units, based on at least one of the block shape information andthe split shape information. According to an embodiment, when the splitshape information indicates to split the first coding unit 400 in ahorizontal direction, the image decoding apparatus 150 may determine asecond coding unit 410 by splitting the first coding unit 400 in ahorizontal direction. A first coding unit, a second coding unit, and athird coding unit used according to an embodiment are terms used tounderstand a relation before and after splitting a coding unit. Forexample, a second coding unit may be determined by splitting a firstcoding unit, and a third coding unit may be determined by splitting thesecond coding unit. It will be understood that a relation among thefirst coding unit, the second coding unit, and the third coding unitfollows the above descriptions.

According to an embodiment, the image decoding apparatus 150 maydetermine to split or not to split the determined second coding unit 410into coding units, based on at least one of the block shape informationand the split shape information. Referring to FIG. 4, the image decodingapparatus 150 may or may not split the non-square second coding unit410, which is determined by splitting the first coding unit 400, intoone or more third coding units 420 a, or 420 b, 420 c, and 420 d basedon at least one of the block shape information and the split shapeinformation.

The image decoding apparatus 150 may obtain at least one of the blockshape information and the split shape information, and determine aplurality of various-shaped second coding units (e.g., 410) by splittingthe first coding unit 400, based on the obtained at least one of theblock shape information and the split shape information, and the secondcoding unit 410 may be split by using the splitting method of the firstcoding unit 400, based on at least one of the block shape informationand the split shape information. According to an embodiment, when thefirst coding unit 400 is split into the second coding units 410 based onat least one of the block shape information and the split shapeinformation of the first coding unit 400, the second coding unit 410 mayalso be split into the third coding units 420 a, or 420 b, 420 c, and420 d based on at least one of the block shape information and the splitshape information of the second coding unit 410. That is, a coding unitmay be recursively split based on at least one of the block shapeinformation and the split shape information of each coding unit. Amethod that may be used to recursively split a coding unit will bedescribed below in relation to various embodiments.

According to an embodiment, the image decoding apparatus 150 maydetermine to split each of the third coding units 420 a, or 420 b, 420c, and 420 d into coding units or not to split the second coding unit410, based on at least one of the block shape information and the splitshape information. According to an embodiment, the image decodingapparatus 150 may split the non-square second coding unit 410 into theodd number of third coding units 420 b, 420 c, and 420 d. The imagedecoding apparatus 150 may put a preset restriction on a preset thirdcoding unit from among the odd number of third coding units 420 b, 420c, and 420 d. For example, the image decoding apparatus 150 may restrictthe third coding unit 420 c at a center position from among the oddnumber of third coding units 420 b, 420 c, and 420 d to be no longersplit or to be split a settable number of times. Referring to FIG. 4,the image decoding apparatus 150 may restrict the third coding unit 420c, which is at the center position from among the odd number of thirdcoding units 420 b, 420 c, and 420 d included in the non-square secondcoding unit 410, to be no longer split, to be split by using a presetsplitting method (e.g., split into only four coding units or split byusing a splitting method of the second coding unit 410), or to be splitonly the preset number of times (e.g., split only n times (where n>0)).However, the restrictions on the third coding unit 420 c at the centerposition are not limited to the above-described examples, and mayinclude various restrictions for decoding the third coding unit 420 c atthe center position differently from the other third coding units 420 band 420 d.

According to an embodiment, the image decoding apparatus 150 may obtainat least one of the block shape information and the split shapeinformation, which is used to split a current coding unit, from a presetposition in the current coding unit.

According to an embodiment, when the current coding unit is split into apreset number of coding units, the image decoding apparatus 150 mayselect one of the coding units. Various methods may be used to selectone of a plurality of coding units, as will be described below inrelation to various embodiments

According to an embodiment, the image decoding apparatus 150 may splitthe current coding unit into a plurality of coding units, and maydetermine a coding unit at a preset position.

FIG. 5 illustrates a method, performed by the image decoding apparatus150, of determining a coding unit of a preset position from among an oddnumber of coding units, according to an embodiment

According to an embodiment, the image decoding apparatus 150 may useinformation indicating positions of the odd number of coding units, todetermine a coding unit at a center position from among the odd numberof coding units. Referring to FIG. 5, the image decoding apparatus 150may determine an odd number of coding units 520 a, 520 b, and 520 c bysplitting the current coding unit 500. The image decoding apparatus 150may determine a coding unit 520 b at a center position by usinginformation about positions of the odd number of coding units 520 a, 520b, and 520 c. For example, the image decoding apparatus 150 maydetermine the coding unit 520 b of the center position by determiningthe positions of the coding units 520 a, 520 b, and 520 c based oninformation indicating positions of preset samples included in thecoding units 520 a, 520 b, and 520 c. In detail, the image decodingapparatus 150 may determine the coding unit 520 b at the center positionby determining the positions of the coding units 520 a, 520 b, and 520 cbased on information indicating positions of top left samples 530 a, 530b, and 530 c of the coding units 520 a, 520 b, and 520 c.

According to an embodiment, the information indicating the positions ofthe top left samples 530 a, 530 b, and 530 c, which are included in thecoding units 520 a, 520 b, and 520 c, respectively, may includeinformation about positions or coordinates of the coding units 520 a,520 b, and 520 c in a picture. According to an embodiment, theinformation indicating the positions of the top left samples 530 a, 530b, and 530 c, which are included in the coding units 520 a, 520 b, and520 c, respectively, may include information indicating widths orheights of the coding units 520 a, 520 b, and 520 c included in thecurrent coding unit 500, and the widths or heights may correspond toinformation indicating differences between the coordinates of the codingunits 520 a, 520 b, and 520 c in the picture. That is, the imagedecoding apparatus 150 may determine the coding unit 520 b at the centerposition by directly using the information about the positions orcoordinates of the coding units 520 a, 520 b, and 520 c in the picture,or by using the information about the widths or heights of the codingunits, which correspond to the difference values between thecoordinates.

According to an embodiment, information indicating the position of thetop left sample 530 a of the upper coding unit 520 a may includecoordinates (xa, ya), information indicating the position of the topleft sample 530 b of the middle coding unit 520 b may includecoordinates (xb, yb), and information indicating the position of the topleft sample 530 c of the lower coding unit 520 c may include coordinates(xc, yc). The image decoding apparatus 150 may determine the middlecoding unit 520 b by using the coordinates of the top left samples 530a, 530 b, and 530 c which are included in the coding units 520 a, 520 b,and 520 c, respectively. For example, when the coordinates of the topleft samples 530 a, 530 b, and 530 c are sorted in an ascending ordescending order, the coding unit 520 b including the coordinates (xb,yb) of the sample 530 b at a center position may be determined as acoding unit at a center position from among the coding units 520 a, 520b, and 520 c determined by splitting the current coding unit 500.However, the coordinates indicating the positions of the top leftsamples 530 a, 530 b, and 530 c may include coordinates indicatingabsolute positions in the picture, or may use coordinates (dxb, dyb)indicating a relative position of the top left sample 530 b of themiddle coding unit 520 b and coordinates (dxc, dyc) indicating arelative position of the top left sample 530 c of the lower coding unit520 c with reference to the position of the top left sample 530 a of theupper coding unit 520 a. A method of determining a coding unit at apreset position by using coordinates of a sample included in the codingunit, as information indicating a position of the sample, is not limitedto the above-described method, and may include various arithmeticmethods capable of using the coordinates of the sample.

According to an embodiment, the image decoding apparatus 150 may splitthe current coding unit 500 into a plurality of coding units 520 a, 520b, and 520 c, and may select one of the coding units 520 a, 520 b, and520 c based on a preset criterion. For example, the image decodingapparatus 150 may select the coding unit 520 b, which has a sizedifferent from that of the others, from among the coding units 520 a,520 b, and 520 c.

According to an embodiment, the image decoding apparatus 150 maydetermine the widths or heights of the coding units 520 a, 520 b, and520 c by using the coordinates (xa, ya) indicating the position of thetop left sample 530 a of the upper coding unit 520 a, the coordinates(xb, yb) indicating the position of the top left sample 530 b of themiddle coding unit 520 b, and the coordinates (xc, yc) indicating theposition of the top left sample 530 c of the lower coding unit 520 c.The image decoding apparatus 150 may determine the respective sizes ofthe coding units 520 a, 520 b, and 520 c by using the coordinates (xa,ya), (xb, yb), and (xc, yc) indicating the positions of the coding units520 a, 520 b, and 520 c.

According to an embodiment, the image decoding apparatus 150 maydetermine the width of the upper coding unit 520 a to be xb-xa anddetermine the height thereof to be yb-ya. According to an embodiment,the image decoding apparatus 150 may determine the width of the middlecoding unit 520 b to be xc-xb and determine the height thereof to beyc-yb. According to an embodiment, the image decoding apparatus 150 maydetermine the width or height of the lower coding unit 520 c by usingthe width or height of the current coding unit 500 or the widths orheights of the upper and middle coding units 520 a and 520 b. The imagedecoding apparatus 150 may determine a coding unit, which has a sizedifferent from that of the others, based on the determined widths andheights of the coding units 520 a, 520 b, and 520 c. Referring to FIG.5, the image decoding apparatus 150 may determine the middle coding unit520 b, which has a size different from the size of the upper and lowercoding units 520 a and 520 c, as the coding unit of the preset position.However, the above-described method, performed by the image decodingapparatus 150, of determining a coding unit having a size different fromthe size of the other coding units merely corresponds to an example ofdetermining a coding unit at a preset position by using the sizes ofcoding units, which are determined based on coordinates of samples, andthus various methods of determining a coding unit at a preset positionby comparing the sizes of coding units, which are determined based oncoordinates of preset samples, may be used.

However, positions of samples considered to determine positions ofcoding units are not limited to the above-described top left positions,and information about random positions of samples included in the codingunits may be used.

According to an embodiment, the image decoding apparatus 150 may selecta coding unit at a preset position from among an odd number of codingunits determined by splitting the current coding unit, considering theshape of the current coding unit. For example, when the current codingunit has a non-square shape, a width of which is longer than a height,the image decoding apparatus 150 may determine the coding unit at thepreset position in a horizontal direction. That is, the image decodingapparatus 150 may determine one of coding units at different positionsin a horizontal direction and put a restriction on the coding unit. Whenthe current coding unit has a non-square shape, a height of which islonger than a width, the image decoding apparatus 150 may determine thecoding unit at the preset position in a vertical direction. That is, theimage decoding apparatus 150 may determine one of coding units atdifferent positions in a vertical direction and may put a restriction onthe coding unit.

According to an embodiment, the image decoding apparatus 150 may useinformation indicating respective positions of an even number of codingunits, to determine the coding unit at the preset position from amongthe even number of coding units. The image decoding apparatus 150 maydetermine an even number of coding units by splitting the current codingunit, and may determine the coding unit at the preset position by usingthe information about the positions of the even number of coding units.An operation related thereto may correspond to the operation ofdetermining a coding unit at a preset position (e.g., a center position)from among an odd number of coding units, which has been described indetail above in relation to FIG. 5, and thus detailed descriptionsthereof are not provided here.

According to an embodiment, when a non-square current coding unit issplit into a plurality of coding units, preset information about acoding unit at a preset position may be used in a splitting operation todetermine the coding unit at the preset position from among theplurality of coding units. For example, the image decoding apparatus 150may use at least one of block shape information and split shapeinformation, which is stored in a sample included in a coding unit at acenter position, in a splitting operation to determine the coding unitat the center position from among the plurality of coding unitsdetermined by splitting the current coding unit.

Referring to FIG. 5, the image decoding apparatus 150 may split thecurrent coding unit 500 into a plurality of coding units 520 a, 520 b,and 520 c based on at least one of the block shape information and thesplit shape information, and may determine a coding unit 520 b at acenter position from among the plurality of the coding units 520 a, 520b, and 520 c. Furthermore, the image decoding apparatus 150 maydetermine the coding unit 520 b at the center position, in considerationof a position from which at least one of the block shape information andthe split shape information is obtained. That is, at least one of theblock shape information and the split shape information of the currentcoding unit 500 may be obtained from the sample 540 at a center positionof the current coding unit 500 and, when the current coding unit 500 issplit into the plurality of coding units 520 a, 520 b, and 520 c basedon at least one of the block shape information and the split shapeinformation, the coding unit 520 b including the sample 540 may bedetermined as the coding unit at the center position. However,information used to determine the coding unit at the center position isnot limited to at least one of the block shape information and the splitshape information, and various types of information may be used todetermine the coding unit at the center position.

According to an embodiment, preset information for identifying thecoding unit at the preset position may be obtained from a preset sampleincluded in a coding unit to be determined. Referring to FIG. 5, theimage decoding apparatus 150 may use at least one of the block shapeinformation and the split shape information, which is obtained from asample at a preset position in the current coding unit 500 (e.g., asample at a center position of the current coding unit 500) to determinea coding unit at a preset position from among the plurality of thecoding units 520 a, 520 b, and 520 c determined by splitting the currentcoding unit 500 (e.g., a coding unit at a center position from among aplurality of split coding units). That is, the image decoding apparatus150 may determine the sample at the preset position by considering ablock shape of the current coding unit 500, determine the coding unit520 b including a sample, from which preset information (e.g., at leastone of the block shape information and the split shape information) maybe obtained, from among the plurality of coding units 520 a, 520 b, and520 c determined by splitting the current coding unit 500, and may put apreset restriction on the coding unit 520 b. Referring to FIG. 5,according to an embodiment, the image decoding apparatus 150 maydetermine the sample 540 at the center position of the current codingunit 500 as the sample from which the preset information may beobtained, and may put a preset restriction on the coding unit 520 bincluding the sample 540, in a decoding operation. However, the positionof the sample from which the preset information may be obtained is notlimited to the above-described position, and may include arbitrarypositions of samples included in the coding unit 520 b to be determinedfor a restriction.

According to an embodiment, the position of the sample from which thepreset information may be obtained may be determined based on the shapeof the current coding unit 500. According to an embodiment, the blockshape information may indicate whether the current coding unit has asquare or non-square shape, and the position of the sample from whichthe preset information may be obtained may be determined based on theshape. For example, the image decoding apparatus 150 may determine asample positioned on a boundary for dividing at least one of a width andheight of the current coding unit in half, as the sample from which thepreset information may be obtained, by using at least one of informationabout the width of the current coding unit and information about theheight of the current coding unit. As another example, when the blockshape information of the current coding unit indicates a non-squareshape, the image decoding apparatus 150 may determine one of samplesadjacent to a boundary for dividing a long side of the current codingunit in half, as the sample from which the preset information may beobtained.

According to an embodiment, when the current coding unit is split into aplurality of coding units, the image decoding apparatus 150 may use atleast one of the block shape information and the split shape informationto determine a coding unit at a preset position from among the pluralityof coding units. According to an embodiment, the image decodingapparatus 150 may obtain at least one of the block shape information andthe split shape information from a sample at a preset position in acoding unit, and may split the plurality of coding units, which aregenerated by splitting the current coding unit, by using at least one ofthe split shape information and the block shape information, which isobtained from the sample of the preset position in each of the pluralityof coding units. That is, a coding unit may be recursively split basedon at least one of the block shape information and the split shapeinformation, which is obtained from the sample at the preset position ineach coding unit. An operation of recursively splitting a coding unithas been described above in relation to FIG. 4, and thus detaileddescriptions thereof will not be provided here.

According to an embodiment, the image decoding apparatus 150 maydetermine one or more coding units by splitting the current coding unit,and may determine an order of decoding the one or more coding units,based on a preset block (e.g., the current coding unit).

FIG. 6 illustrates an order of processing a plurality of coding unitswhen the image decoding apparatus 150 determines the plurality of codingunits by splitting a current coding unit, according to an embodiment.

According to an embodiment, the image decoding apparatus 150 maydetermine second coding units 610 a and 610 b by splitting a firstcoding unit 600 in a vertical direction, may determine second codingunits 630 a and 630 b by splitting the first coding unit 600 in ahorizontal direction, or may determine second coding units 650 a, 650 b,650 c, and 650 d by splitting the first coding unit 600 in vertical andhorizontal directions, based on block shape information and split shapeinformation.

Referring to FIG. 6, the image decoding apparatus 150 may determine toprocess the second coding units 610 a and 610 b, which are determined bysplitting the first coding unit 600 in a vertical direction, in ahorizontal direction order 610 c. The image decoding apparatus 150 maydetermine to process the second coding units 630 a and 630 b, which aredetermined by splitting the first coding unit 600 in a horizontaldirection, in a vertical direction order 630 c. The image decodingapparatus 150 may determine to process the second coding units 650 a,650 b, 650 c, and 650 d, which are determined by splitting the firstcoding unit 600 in vertical and horizontal directions, according to apreset order (e.g., a raster scan order or Z-scan order 650 e) by whichcoding units in a row are processed and then coding units in a next roware processed.

According to an embodiment, the image decoding apparatus 150 mayrecursively split coding units. Referring to FIG. 6, the image decodingapparatus 150 may determine a plurality of coding units 610 a, 610 b,630 a, 630 b, 650 a, 650 b, 650 c, and 650 d by splitting the firstcoding unit 600, and may recursively split each of the determinedplurality of coding units 610 a, 610 b, 630 a, 630 b, 650 a, 650 b, 650c, and 650 d. A splitting method of the plurality of coding units 610 a,610 b, 630 a, 630 b, 650 a, 650 b, 650 c, and 650 d may correspond to asplitting method of the first coding unit 600. As such, each of theplurality of coding units 610 a, 610 b, 630 a, 630 b, 650 a, 650 b, 650c, and 650 d may be independently split into a plurality of codingunits. Referring to FIG. 6, the image decoding apparatus 150 maydetermine the second coding units 610 a and 610 b by splitting the firstcoding unit 600 in a vertical direction, and may determine toindependently split or not to split each of the second coding units 610a and 610 b.

According to an embodiment, the image decoding apparatus 150 maydetermine third coding units 620 a and 620 b by splitting the leftsecond coding unit 610 a in a horizontal direction, and may not splitthe right second coding unit 610 b.

According to an embodiment, a processing order of coding units may bedetermined based on an operation of splitting a coding unit. In otherwords, a processing order of split coding units may be determined basedon a processing order of coding units immediately before being split.The image decoding apparatus 150 may determine a processing order of thethird coding units 620 a and 620 b determined by splitting the leftsecond coding unit 610 a, independently of the right second coding unit610 b. Because the third coding units 620 a and 620 b are determined bysplitting the left second coding unit 610 a in a horizontal direction,the third coding units 620 a and 620 b may be processed in a verticaldirection order 620 c. Because the left and right second coding units610 a and 610 b are processed in the horizontal direction order 610 c,the right second coding unit 610 b may be processed after the thirdcoding units 620 a and 620 b included in the left second coding unit 610a are processed in the vertical direction order 620 c. An operation ofdetermining a processing order of coding units based on a coding unitbefore being split is not limited to the above-described example, andvarious methods may be used to independently process coding units, whichare split and determined to various shapes, in a preset order.

FIG. 7 illustrates a process, performed by the image decoding apparatus150, of determining that a current coding unit is to be split into anodd number of coding units, when the coding units are not processable ina preset order, according to an embodiment.

According to an embodiment, the image decoding apparatus 150 maydetermine whether the current coding unit is to be split into an oddnumber of coding units, based on obtained block shape information andsplit shape information. Referring to FIG. 7, a square first coding unit700 may be split into non-square second coding units 710 a and 710 b,and the second coding units 710 a and 710 b may be independently splitinto third coding units 720 a and 720 b, and 720 c to 720 e. Accordingto an embodiment, the image decoding apparatus 150 may determine aplurality of third coding units 720 a and 720 b by splitting the leftsecond coding unit 710 a in a horizontal direction, and may split theright second coding unit 710 b into an odd number of third coding units720 c to 720 e.

According to an embodiment, the image decoding apparatus 150 maydetermine whether any coding unit is to be split into an odd number ofcoding units, by determining whether the third coding units 720 a and720 b, and 720 c to 720 e are processable in a preset order. Referringto FIG. 7, the image decoding apparatus 150 may determine the thirdcoding units 720 a and 720 b, and 720 c to 720 e by recursivelysplitting the first coding unit 700. The image decoding apparatus 150may determine whether any of the first coding unit 700, the secondcoding units 710 a and 710 b, and the third coding units 720 a and 720b, and 720 c, 720 d, and 720 e is to be split into an odd number ofcoding units, based on at least one of the block shape information andthe split shape information. For example, a second coding unit locatedin the right from among the second coding units 710 a and 710 b may besplit into an odd number of third coding units 720 c, 720 d, and 720 e.A processing order of a plurality of coding units included in the firstcoding unit 700 may be a preset order (e.g., a Z-scan order 730), andthe image decoding apparatus 70 may determine whether the third codingunits 720 c, 720 d, and 720 e, which are determined by splitting theright second coding unit 710 b into an odd number of coding units,satisfy a condition for processing in the preset order.

According to an embodiment, the image decoding apparatus 150 maydetermine whether the third coding units 720 a and 720 b, and 720 c, 720d, and 720 e included in the first coding unit 700 satisfy the conditionfor processing in the preset order, and the condition relates to whetherat least one of a width and height of the second coding units 710 a and710 b is to be divided in half along a boundary of the third codingunits 720 a and 720 b, and 720 c, 720 d, and 720 e. For example, thethird coding units 720 a and 720 b determined by dividing the height ofthe non-square left second coding unit 710 a in half satisfy thecondition. However, because boundaries of the third coding units 720 c,720 d, and 720 e determined by splitting the right second coding unit710 b into three coding units do not divide the width or height of theright second coding unit 710 b in half, it may be determined that thethird coding units 720 c, 720 d, and 720 e do not satisfy the condition.When the condition is not satisfied as described above, the imagedecoding apparatus 150 may decide disconnection of a scan order, anddetermine that the right second coding unit 710 b is to be split into anodd number of coding units, based on a result of the decision. Accordingto an embodiment, when a coding unit is split into an odd number ofcoding units, the image decoding apparatus 150 may put a presetrestriction on a coding unit at a preset position among the split codingunits. The restriction or the preset position has been described abovein relation to various embodiments, and thus detailed descriptionsthereof will not be provided here.

FIG. 8 illustrates a process, performed by the image decoding apparatus150, of determining at least one coding unit by splitting a first codingunit 800, according to an embodiment. According to an embodiment, theimage decoding apparatus 150 may split the first coding unit 800, basedon at least one of block shape information and split shape information,which is obtained by the receiver 160. The square first coding unit 800may be split into four square coding units, or may be split into aplurality of non-square coding units. For example, referring to FIG. 8,when the block shape information indicates that the first coding unit800 has a square shape and the split shape information indicates tosplit the first coding unit 800 into non-square coding units, the imagedecoding apparatus 150 may split the first coding unit 800 into aplurality of non-square coding units. In detail, when the split shapeinformation indicates to determine an odd number of coding units bysplitting the first coding unit 800 in a horizontal direction or avertical direction, the image decoding apparatus 150 may split thesquare first coding unit 800 into an odd number of coding units, e.g.,second coding units 810 a, 810 b, and 810 c determined by splitting thesquare first coding unit 800 in a vertical direction or second codingunits 820 a, 820 b, and 820 c determined by splitting the square firstcoding unit 800 in a horizontal direction.

According to an embodiment, the image decoding apparatus 150 maydetermine whether the second coding units 810 a, 810 b, 810 c, 820 a,820 b, and 820 c included in the first coding unit 800 satisfy acondition for processing in a preset order, and the condition relates towhether at least one of a width and height of the first coding unit 800is to be divided in half along a boundary of the second coding units 810a, 810 b, 810 c, 820 a, 820 b, and 820 c. Referring to FIG. 8, becauseboundaries of the second coding units 810 a, 810 b, and 810 c determinedby splitting the square first coding unit 800 in a vertical direction donot divide the height of the first coding unit 800 in half, it may bedetermined that the first coding unit 800 does not satisfy the conditionfor processing in the preset order. In addition, because boundaries ofthe second coding units 820 a, 820 b, and 820 c determined by splittingthe square first coding unit 800 in a horizontal direction do not dividethe width of the first coding unit 800 in half, it may be determinedthat the first coding unit 800 does not satisfy the condition forprocessing in the preset order. When the condition is not satisfied asdescribed above, the image decoding apparatus 150 may decidedisconnection of a scan order, and may determine that the first codingunit 800 is to be split into an odd number of coding units, based on aresult of the decision. According to an embodiment, when a coding unitis split into an odd number of coding units, the image decodingapparatus 150 may put a preset restriction on a coding unit at a presetposition from among the split coding units. The restriction or thepreset position has been described above in relation to variousembodiments, and thus detailed descriptions thereof will not be providedherein.

According to an embodiment, the image decoding apparatus 150 maydetermine various-shaped coding units by splitting a first coding unit.

Referring to FIG. 8, the image decoding apparatus 150 may split thesquare first coding unit 800 or a non-square first coding unit 830 or850 into various-shaped coding units.

FIG. 9 illustrates that a shape into which a second coding unit issplittable by the image decoding apparatus 150 is restricted when thesecond coding unit having a non-square shape, which is determined bysplitting a first coding unit 900, satisfies a preset condition,according to an embodiment.

According to an embodiment, the image decoding apparatus 150 maydetermine to split the square first coding unit 900 into non-squaresecond coding units 910 a, 910 b, 920 a, and 920 b, based on at leastone of block shape information and split shape information, which isobtained by the receiver 160. The second coding units 910 a, 910 b, 920a, and 920 b may be independently split. As such, the image decodingapparatus 150 may determine to split or not to split the first codingunit 900 into a plurality of coding units, based on at least one of theblock shape information and the split shape information of each of thesecond coding units 910 a, 910 b, 920 a, and 920 b. According to anembodiment, the image decoding apparatus 150 may determine third codingunits 912 a and 912 b by splitting the non-square left second codingunit 910 a, which is determined by splitting the first coding unit 900in a vertical direction, in a horizontal direction. However, when theleft second coding unit 910 a is split in a horizontal direction, theimage decoding apparatus 150 may restrict the right second coding unit910 b to not be split in a horizontal direction in which the left secondcoding unit 910 a is split. When third coding units 914 a and 914 b aredetermined by splitting the right second coding unit 910 b in a samedirection, because the left and right second coding units 910 a and 910b are independently split in a horizontal direction, the third codingunits 912 a, 912 b, 914 a, and 914 b may be determined. However, thiscase serves equally as a case in which the image decoding apparatus 150splits the first coding unit 900 into four square second coding units930 a, 930 b, 930 c, and 930 d, based on at least one of the block shapeinformation and the split shape information, and may be inefficient interms of image decoding.

According to an embodiment, the image decoding apparatus 150 maydetermine third coding units 922 a, 922 b, 924 a, and 924 b by splittingthe non-square second coding unit 920 a or 920 b, which is determined bysplitting the first coding unit 900 in a horizontal direction, in avertical direction. However, when a second coding unit (e.g., the uppersecond coding unit 920 a) is split in a vertical direction, for theabove-described reason, the image decoding apparatus 150 may restrictthe other second coding unit (e.g., the lower second coding unit 920 b)to not be split in a vertical direction in which the upper second codingunit 920 a is split.

FIG. 18 illustrates a process, performed by the image decoding apparatus150, of splitting a square coding unit when split shape informationindicates that the square coding unit is not to be split into foursquare coding units, according to an embodiment.

According to an embodiment, the image decoding apparatus 150 maydetermine second coding units 1010 a, 1010 b, 1020 a, 1020 b, etc. bysplitting a first coding unit 1000, based on at least one of block shapeinformation and split shape information. The split shape information mayinclude information about various methods of splitting a coding unitbut, the information about various splitting methods may not includeinformation for splitting a coding unit into four square coding units.According to such split shape information, the image decoding apparatus150 may not split the first square coding unit 1000 into four squaresecond coding units 1030 a, 1030 b, 1030 c, and 1030 d. The imagedecoding apparatus 150 may determine the non-square second coding units1010 a, 1010 b, 1020 a, 1020 b, etc., based on the split shapeinformation.

According to an embodiment, the image decoding apparatus 150 mayindependently split the non-square second coding units 1010 a, 1010 b,1020 a, 1020 b, etc. Each of the second coding units 1010 a, 1010 b,1020 a, 1020 b, etc. may be recursively split in a preset order, andthis splitting method may correspond to a method of splitting the firstcoding unit 1000, based on at least one of the block shape informationand the split shape information.

For example, the image decoding apparatus 150 may determine square thirdcoding units 1012 a and 1012 b by splitting the left second coding unit1010 a in a horizontal direction, and may determine square third codingunits 1014 a and 1014 b by splitting the right second coding unit 1010 bin a horizontal direction. Furthermore, the image decoding apparatus 150may determine square third coding units 1016 a, 1016 b, 1016 c, and 1016d by splitting both of the left and right second coding units 1010 a and1010 b in a horizontal direction. In this case, coding units having thesame shape as the four square second coding units 1030 a, 1030 b, 1030c, and 1030 d split from the first coding unit 1000 may be determined.

As another example, the image decoding apparatus 150 may determinesquare third coding units 1022 a and 1022 b by splitting the uppersecond coding unit 1020 a in a vertical direction, and may determinesquare third coding units 1024 a and 1024 b by splitting the lowersecond coding unit 1020 b in a vertical direction. Furthermore, theimage decoding apparatus 150 may determine square third coding units1022 a, 1022 b, 1024 a, and 1024 bby splitting both of the upper andlower second coding units 1020 a and 1020 b in a vertical direction. Inthis case, coding units having the same shape as the four square secondcoding units 1030 a, 1030 b, 1030 c, and 1030 d split from the firstcoding unit 1000 may be determined.

FIG. 11 illustrates that a processing order between a plurality ofcoding units may be changed depending on a process of splitting a codingunit, according to an embodiment.

According to an embodiment, the image decoding apparatus 150 may split afirst coding unit 1100, based on block shape information and split shapeinformation. When the block shape information indicates a square shapeand the split shape information indicates to split the first coding unit1100 in at least one of horizontal and vertical directions, the imagedecoding apparatus 150 may determine second coding units 1110 a, 1110 b,1120 a, and 1120 b by splitting the first coding unit 1100. Referring toFIG. 11, the non-square second coding units 1110 a, 1110 b, 1120 a, and1120 b determined by splitting the first coding unit 1100 in only ahorizontal direction or vertical direction may be independently splitbased on the block shape information and the split shape information ofeach coding unit. For example, the image decoding apparatus 150 maydetermine third coding units 1116 a, 1116 b, 1116 c, and 1116 d bysplitting the second coding units 1110 a and 1110 b, which are generatedby splitting the first coding unit 1100 in a vertical direction, in ahorizontal direction, and may determine third coding units 1126 a, 1126b, 1126 c, and 1126 d by splitting the second coding units 1120 a and1120 b, which are generated by splitting the first coding unit 1100 in ahorizontal direction, in a vertical direction. An operation of splittingthe second coding units 1110 a, 1110 b, 1120 a, and 1120 b has beendescribed above in relation to FIG. 9, and thus detailed descriptionsthereof will not be provided herein.

According to an embodiment, the image decoding apparatus 150 may processcoding units in a preset order. An operation of processing coding unitsin a preset order has been described above in relation to FIG. 6, andthus detailed descriptions thereof will not be provided herein.Referring to FIG. 11, the image decoding apparatus 150 may determinefour square third coding units 1116 a, 1116 b, 1116 c, and 1116 d, and1126 a, 1126 b, 1126 c, and 1126 d by splitting the square first codingunit 1100. According to an embodiment, the image decoding apparatus 150may determine processing orders of the third coding units 1116 a, 1116b, 1116 c, and 1116 d, and 1126 a, 1126 b, 1126 c, and 1126 d based on asplitting method of the first coding unit 1100.

According to an embodiment, the image decoding apparatus 150 maydetermine the third coding units 1116 a, 1116 b, 1116 c, and 1116 d bysplitting the second coding units 1110 a and 1110 b generated bysplitting the first coding unit 1100 in a vertical direction, in ahorizontal direction, and may process the third coding units 1116 a,1116 b, 1116 c, and 1116 d in a processing order 1117 for initiallyprocessing the third coding units 1116 a and, which are included in theleft second coding unit 1110 a, in a vertical direction and thenprocessing the third coding unit 1116 b and 1116 d, which are includedin the right second coding unit 1110 b, in a vertical direction.

According to an embodiment, the image decoding apparatus 150 maydetermine the third coding units 1126 a, 1126 b, 1126 c, and 1126 d bysplitting the second coding units 1120 a and 1120 b generated bysplitting the first coding unit 1100 in a horizontal direction, in avertical direction, and may process the third coding units 1126 a, 1126b, 1126 c, and 1126 d in a processing order 1127 for initiallyprocessing the third coding units 1126 a and 1126 b, which are includedin the upper second coding unit 1120 a, in a horizontal direction andthen processing the third coding unit 1126 c and 1126 d, which areincluded in the lower second coding unit 1120 b, in a horizontaldirection.

Referring to FIG. 11, the square third coding units 1116 a, 1116 b, 1116c, and 1116 d, and 1126 a, 1126 b, 1126 c, and 1126 d may be determinedby splitting the second coding units 1110 a, 1110 b, 1120 a, and 1120 b,respectively. Although the second coding units 1110 a and 1110 b aredetermined by splitting the first coding unit 1100 in a verticaldirection differently from the second coding units 1120 a and 1120 bwhich are determined by splitting the first coding unit 1100 in ahorizontal direction, the third coding units 1116 a, 1116 b, 1116 c, and1116 d, and 1126 a, 1126 b, 1126 c, and 1126 d split therefromeventually show same-shaped coding units split from the first codingunit 1100. As such, by recursively splitting a coding unit in differentmanners based on at least one of the block shape information and thesplit shape information, the image decoding apparatus 150 may process aplurality of coding units in different orders even when the coding unitsare eventually determined to be the same shape.

FIG. 12 illustrates a process of determining a depth of a coding unit asa shape and size of the coding unit change, when the coding unit isrecursively split such that a plurality of coding units are determined,according to an embodiment.

According to an embodiment, the image decoding apparatus 150 maydetermine the depth of the coding unit, based on a preset criterion. Forexample, the preset criterion may be the length of a long side of thecoding unit. When the length of a long side of a coding unit beforebeing split is 2n times (n>0) the length of a long side of a splitcurrent coding unit, the image decoding apparatus 150 may determine thata depth of the current coding unit is increased from a depth of thecoding unit before being split, by n. In the following description, acoding unit having an increased depth is expressed as a coding unit of adeeper depth.

Referring to FIG. 12, according to an embodiment, the image decodingapparatus 150 may determine a second coding unit 1202 and a third codingunit 1204 of deeper depths by splitting a square first coding unit 1200based on block shape information indicating a square shape (for example,the block shape information may be expressed as ‘0: SQUARE’). Assumingthat the size of the square first coding unit 1200 is 2N×2N, the secondcoding unit 1202 determined by dividing a width and height of the firstcoding unit 1200 to ½ may have a size of N×N. Furthermore, the thirdcoding unit 1204 determined by dividing a width and height of the secondcoding unit 1202 to ½ may have a size of N/2×N/2. In this case, a widthand height of the third coding unit 1204 are ½ times those of the firstcoding unit 1200. When a depth of the first coding unit 1200 is D, adepth of the second coding unit 1202, the width and height of which are1/21 times those of the first coding unit 1200, may be D+1, and a depthof the third coding unit 1204, the width and height of which are ½ timesthose of the first coding unit 1200, may be D+2.

According to an embodiment, the image decoding apparatus 150 maydetermine a second coding unit 1212 or 1222 and a third coding unit 1214or 1224 of deeper depths by splitting a non-square first coding unit1210 or 1220 based on block shape information indicating a non-squareshape (for example, the block shape information may be expressed as ‘1:NS_VER’ indicating a non-square shape, a height of which is longer thana width, or as ‘2: NS_HOR’ indicating a non-square shape, a width ofwhich is longer than a height).

The image decoding apparatus 150 may determine a second coding unit1202, 1212, or 1222 by dividing at least one of a width and height ofthe first coding unit 1210 having a size of N×2N. That is, the imagedecoding apparatus 150 may determine the second coding unit 1202 havinga size of N×N or the second coding unit 1222 having a size of N×N/2 bysplitting the first coding unit 1210 in a horizontal direction, or maydetermine the second coding unit 1212 having a size of N/2×N bysplitting the first coding unit 1210 in horizontal and verticaldirections.

According to an embodiment, the image decoding apparatus 150 maydetermine the second coding unit 1202, 1212, or 1222 by dividing atleast one of a width and height of the first coding unit 1220 having asize of 2N×N. That is, the image decoding apparatus 150 may determinethe second coding unit 1202 having a size of N×N or the second codingunit 1212 having a size of N/2×N by splitting the first coding unit 1220in a vertical direction, or may determine the second coding unit 1222having a size of N×N/2 by splitting the first coding unit 1220 inhorizontal and vertical directions.

According to an embodiment, the image decoding apparatus 150 maydetermine a third coding unit 1204, 1214, or 1224 by dividing at leastone of a width and height of the second coding unit 1202 having a sizeof N×N. That is, the image decoding apparatus 150 may determine thethird coding unit 1204 having a size of N/2×N/2, the third coding unit1214 having a size of N/2×N/2, or the third coding unit 1224 having asize of N/2×N/2 by splitting the second coding unit 1202 in vertical andhorizontal directions.

According to an embodiment, the image decoding apparatus 150 maydetermine the third coding unit 1204, 1214, or 1224 by dividing at leastone of a width and height of the second coding unit 1212 having a sizeof N/2×N. That is, the image decoding apparatus 150 may determine thethird coding unit 1204 having a size of N/2×N/2 or the third coding unit1224 having a size of N/2×N/2 by splitting the second coding unit 1212in a horizontal direction, or may determine the third coding unit 1214having a size of N/2×N/2 by splitting the second coding unit 1212 invertical and horizontal directions.

According to an embodiment, the image decoding apparatus 150 maydetermine the third coding unit 1204, 1214, or 1224 by dividing at leastone of a width and height of the second coding unit 1212 having a sizeof N×N/2. That is, the image decoding apparatus 150 may determine thethird coding unit 1204 having a size of N/2×N/2 or the third coding unit1214 having a size of N/2×N/2 by splitting the second coding unit 1222in a vertical direction, or may determine the third coding unit 1224having a size of N/2×N/2 by splitting the second coding unit 1222 invertical and horizontal directions.

According to an embodiment, the image decoding apparatus 150 may splitthe square coding unit 1200, 1202, or 1204 in a horizontal or verticaldirection. For example, the image decoding apparatus 150 may determinethe first coding unit 1210 having a size of N×2N by splitting the firstcoding unit 1200 having a size of 2N×2N in a vertical direction, or maydetermine the first coding unit 1220 having a size of 2N×N by splittingthe first coding unit 1200 in a horizontal direction. According to anembodiment, when a depth is determined based on the length of thelongest side of a coding unit, a depth of a coding unit determined bysplitting the first coding unit 1200, 1202 or 1204 having a size of2N×2N in a horizontal or vertical direction may be the same as the depthof the first coding unit 1200, 1202 or 1204.

According to an embodiment, a width and height of the third coding unit1214 or 1224 may be ½ times those of the first coding unit 1210 or 1220.When a depth of the first coding unit 1210 or 1220 is D, a depth of thesecond coding unit 1212 or 1222, the width and height of which are ½times those of the first coding unit 1210 or 1220, may be D+1, and adepth of the third coding unit 1214 or 1224, the width and height ofwhich are ½ times those of the first coding unit 1210 or 1220, may beD+2.

FIG. 13 illustrates depths that are determinable based on shapes andsizes of coding units, and part indexes (PIDs) that are fordistinguishing the coding units, according to an embodiment.

According to an embodiment, the image decoding apparatus 150 maydetermine various-shape second coding units by splitting a square firstcoding unit 1300. Referring to FIG. 13, the image decoding apparatus 150may determine second coding units 1302 a and 1302 b, 1304 a and 1304 b,and 1306 a, 1306 b, 1306 c, and 1306 d by splitting the first codingunit 1300 in at least one of vertical and horizontal directions based onsplit shape information. That is, the image decoding apparatus 150 maydetermine the second coding units 1302 a and 1302 b, 1304 a and 1304 b,and 1306 a, 1306 b, 1306 c, and 1306 d, based on the split shapeinformation of the first coding unit 1300.

According to an embodiment, a depth of the second coding units 1302 aand 1302 b, 1304 a and 1304 b, and 1306 a, 1306 b, 1306 c, and 1306 d,which are determined based on the split shape information of the squarefirst coding unit 1300, may be determined based on the length of a longside thereof. For example, because the length of a side of the squarefirst coding unit 1300 equals the length of a long side of thenon-square second coding units 1302 a and 1302 b, and 1304 a and 1304 b,the first coding unit 1300 and the non-square second coding units 1302 aand 1302 b, and 1304 a and 1304 b may have the same depth, e.g., D.However, when the image decoding apparatus 150 splits the first codingunit 1300 into the four square second coding units 1306 a, 1306 b, 1306c, and 1306 d based on the split shape information, because the lengthof a side of the square second coding units 1306 a, 1306 b, 1306 c, and1306 d is ½ times the length of a side of the first coding unit 1300, adepth of the second coding units 1306 a, 1306 b, 1306 c, and 1306 d maybe D+1 which is deeper than the depth D of the first coding unit 1300 by1.

According to an embodiment, the image decoding apparatus 150 maydetermine a plurality of second coding units 1312 a and 1312 b, and 1314a, 1314 b, and 1314 c by splitting a first coding unit 1310, a height ofwhich is longer than a width, in a horizontal direction based on thesplit shape information. According to an embodiment, the image decodingapparatus 150 may determine a plurality of second coding units 1322 aand 1322 b, and 1324 a, 1324 b, and 1324 c by splitting a first codingunit 1320, a width of which is longer than a height, in a verticaldirection based on the split shape information.

According to an embodiment, a depth of the second coding units 1312 aand 1312 b, 1314 a, 1314 b, and 1314 c, 1322 a and 1322 b, and 1324 a,1324 b, and 1324 c, which are determined based on the split shapeinformation of the non-square first coding unit 1310 or 1320, may bedetermined based on the length of a long side thereof. For example,because the length of a side of the square second coding units 1312 aand 1312 b is ½ times the length of a long side of the first coding unit1310 having a non-square shape, a height of which is longer than awidth, a depth of the square second coding units 1312 a and 1312 b isD+1 which is deeper than the depth D of the non-square first coding unit1310 by 1.

Furthermore, the image decoding apparatus 150 may split the non-squarefirst coding unit 1310 into an odd number of second coding units 1314 a,1314 b, and 1314 c based on the split shape information. The odd numberof second coding units 1314 a, 1314 b, and 1314 c may include thenon-square second coding units 1314 a and 1314 c and the square secondcoding unit 1314 b. In this case, because the length of a long side ofthe non-square second coding units 1314 a and 1314 c and the length of aside of the square second coding unit 1314 b are ½ times the length of along side of the first coding unit 1310, a depth of the second codingunits 1314 a, 1314 b, and 1314 c may be D+1 which is deeper than thedepth D of the non-square first coding unit 1310 by 1. The imagedecoding apparatus 150 may determine depths of coding units split fromthe first coding unit 1320 having a non-square shape, a width of whichis longer than a height, by using the above-described method ofdetermining depths of coding units split from the first coding unit1310.

According to an embodiment, the image decoding apparatus 150 maydetermine PIDs for identifying split coding units, based on a size ratiobetween the coding units when an odd number of split coding units do nothave equal sizes. Referring to FIG. 13, a coding unit 1314 b of a centerposition among an odd number of split coding units 1314 a, 1314 b, and1314 c may have a width equal to that of the other coding units 1314 aand 1314 c and a height which is two times that of the other codingunits 1314 a and 1314 c. That is, in this case, the coding unit 1314 bat the center position may include two of the other coding unit 1314 aor 1314 c. Therefore, when a PID of the coding unit 1314 b at the centerposition is 1 based on a scan order, a PID of the coding unit 1314 clocated next to the coding unit 1314 b may be increased by 2 and thusmay be 3. That is, discontinuity in PID values may be present. Accordingto an embodiment, the image decoding apparatus 150 may determine whetheran odd number of split coding units do not have equal sizes, based onwhether discontinuity is present in PIDs for identifying the splitcoding units.

According to an embodiment, the image decoding apparatus 150 maydetermine whether to use a specific splitting method, based on PIDvalues for identifying a plurality of coding units determined bysplitting a current coding unit. Referring to FIG. 13, the imagedecoding apparatus 150 may determine an even number of coding units 1312a and 1312 b or an odd number of coding units 1314 a, 1314 b, and 1314 cby splitting the first coding unit 1310 having a rectangular shape, aheight of which is longer than a width. The image decoding apparatus 150may use PIDs to identify respective coding units. According to anembodiment, the PID may be obtained from a sample of a preset positionof each coding unit (e.g., a top left sample).

According to an embodiment, the image decoding apparatus 150 maydetermine a coding unit at a preset position from among the split codingunits, by using the PIDs for distinguishing the coding units. Accordingto an embodiment, when the split shape information of the first codingunit 1310 having a rectangular shape, a height of which is longer than awidth, indicates to split a coding unit into three coding units, theimage decoding apparatus 150 may split the first coding unit 1310 intothree coding units 1314 a, 1314 b, and 1314 c. The image decodingapparatus 150 may assign a PID to each of the three coding units 1314 a,1314 b, and 1314 c. The image decoding apparatus 150 may compare PIDs ofan odd number of split coding units to determine a coding unit at acenter position from among the coding units. The image decodingapparatus 150 may determine the coding unit 1314 b having a PIDcorresponding to a middle value among the PIDs of the coding units, asthe coding unit at the center position from among the coding unitsdetermined by splitting the first coding unit 1310. According to anembodiment, the image decoding apparatus 150 may determine PIDs fordistinguishing split coding units, based on a size ratio between thecoding units when the split coding units do not have equal sizes.Referring to FIG. 13, the coding unit 1314 b generated by splitting thefirst coding unit 1310 may have a width equal to that of the othercoding units 1314 a and 1314 c and a height which is two times that ofthe other coding units 1314 a and 1314 c. In this case, when the PID ofthe coding unit 1314 b at the center position is 1, the PID of thecoding unit 1314 c located next to the coding unit 1314 b may beincreased by 2 and thus may be 3. When the PID is not uniformlyincreased as described above, the image decoding apparatus 150 maydetermine that a coding unit is split into a plurality of coding unitsincluding a coding unit having a size different from that of the othercoding units. According to an embodiment, when the split shapeinformation indicates to split a coding unit into an odd number ofcoding units, the image decoding apparatus 150 may split a currentcoding unit in such a manner that a coding unit of a preset positionamong an odd number of coding units (e.g., a coding unit of a centreposition) has a size different from that of the other coding units. Inthis case, the image decoding apparatus 150 may determine the codingunit of the centre position, which has a different size, by using PIDsof the coding units. However, the PIDs and the size or position of thecoding unit of the preset position are not limited to theabove-described examples, and various PIDs and various positions andsizes of coding units may be used.

According to an embodiment, the image decoding apparatus 150 may use apreset data unit where a coding unit starts to be recursively split.

FIG. 14 illustrates that a plurality of coding units are determinedbased on a plurality of preset data units included in a picture,according to an embodiment.

According to an embodiment, a preset data unit may be defined as a dataunit where a coding unit starts to be recursively split by using atleast one of block shape information and split shape information. Thatis, the preset data unit may correspond to a coding unit of an uppermostdepth, which is used to determine a plurality of coding units split froma current picture. In the following descriptions, for convenience ofexplanation, the preset data unit is referred to as a reference dataunit.

According to an embodiment, the reference data unit may have a presetsize and a preset size shape. According to an embodiment, a referencecoding unit may include M×N samples. Herein, M and N may be equal toeach other, and may be integers expressed as powers of 2. That is, thereference data unit may have a square or non-square shape, and may besplit into an integer number of coding units.

According to an embodiment, the image decoding apparatus 150 may splitthe current picture into a plurality of reference data units. Accordingto an embodiment, the image decoding apparatus 150 may split theplurality of reference data units, which are split from the currentpicture, by using splitting information about each reference data unit.The operation of splitting the reference data unit may correspond to asplitting operation using a quadtree structure.

According to an embodiment, the image decoding apparatus 150 maypreviously determine the minimum size allowed for the reference dataunits included in the current picture. Accordingly, the image decodingapparatus 150 may determine various reference data units having sizesequal to or greater than the minimum size, and may determine one or morecoding units by using the block shape information and the split shapeinformation with reference to the determined reference data unit.

Referring to FIG. 14, the image decoding apparatus 150 may use a squarereference coding unit 1400 or a non-square reference coding unit 1402.According to an embodiment, the shape and size of reference coding unitsmay be determined based on various data units capable of including oneor more reference coding units (e.g., sequences, pictures, slices, slicesegments, largest coding units, or the like).

According to an embodiment, the receiver 160 of the image decodingapparatus 150 may obtain, from a bitstream, at least one of referencecoding unit shape information and reference coding unit size informationwith respect to each of the various data units. An operation ofsplitting the square reference coding unit 1400 into one or more codingunits has been described above in relation to the operation of splittingthe current coding unit 1000 of FIG. 10, and an operation of splittingthe non-square reference coding unit 1402 into one or more coding unitshas been described above in relation to the operation of splitting thecurrent coding unit 1100 or 1150 of FIG. 11. Thus, detailed descriptionsthereof will not be provided herein.

According to an embodiment, the image decoding apparatus 150 may use aPID for identifying the size and shape of reference coding units, todetermine the size and shape of reference coding units according to somedata units previously determined based on a preset condition. That is,the receiver 160 may obtain, from the bitstream, only the PID foridentifying the size and shape of reference coding units with respect toeach slice, slice segment, or largest coding unit which is a data unitsatisfying a preset condition (e.g., a data unit having a size equal toor smaller than a slice) among the various data units (e.g., sequences,pictures, slices, slice segments, largest coding units, or the like).The image decoding apparatus 150 may determine the size and shape ofreference data units with respect to each data unit, which satisfies thepreset condition, by using the PID. When the reference coding unit shapeinformation and the reference coding unit size information are obtainedand used from the bitstream according to each data unit having arelatively small size, efficiency of using the bitstream may not behigh, and therefore, only the PID may be obtained and used instead ofdirectly obtaining the reference coding unit shape information and thereference coding unit size information. In this case, at least one ofthe size and shape of reference coding units corresponding to the PIDfor identifying the size and shape of reference coding units may bepreviously determined. That is, the image decoding apparatus 150 maydetermine at least one of the size and shape of reference coding unitsincluded in a data unit serving as a unit for obtaining the PID, byselecting the previously determined at least one of the size and shapeof reference coding units based on the PID.

According to an embodiment, the image decoding apparatus 150 may use oneor more reference coding units included in a largest coding unit. Thatis, a largest coding unit split from a picture may include one or morereference coding units, and coding units may be determined byrecursively splitting each reference coding unit. According to anembodiment, at least one of a width and height of the largest codingunit may be integer times at least one of the width and height of thereference coding units. According to an embodiment, the size ofreference coding units may be obtained by splitting the largest codingunit n times based on a quadtree structure. That is, the image decodingapparatus 150 may determine the reference coding units by splitting thelargest coding unit n times based on a quadtree structure, and may splitthe reference coding unit based on at least one of the block shapeinformation and the split shape information according to variousembodiments.

FIG. 15 illustrates a processing block serving as a unit for determininga determination order of reference coding units included in a picture1500, according to an embodiment.

According to an embodiment, the image decoding apparatus 150 maydetermine one or more processing blocks split from a picture. Theprocessing block is a data unit including one or more reference codingunits split from a picture, and the one or more reference coding unitsincluded in the processing block may be determined according to aspecific order. That is, a determination order of one or more referencecoding units determined in each processing block may correspond to oneof various types of orders for determining reference coding units, andmay vary depending on the processing block. The determination order ofreference coding units, which is determined with respect to eachprocessing block, may be one of various orders, e.g., raster scan order,Z-scan, N-scan, up-right diagonal scan, horizontal scan, and verticalscan, but is not limited to the above-mentioned scan orders.

According to an embodiment, the image decoding apparatus 150 may obtainprocessing block size information and may determine the size of one ormore processing blocks included in the picture. The image decodingapparatus 150 may obtain the processing block size information from abitstream and may determine the size of one or more processing blocksincluded in the picture. The size of processing blocks may be a presetsize of data units, which is indicated by the processing block sizeinformation.

According to an embodiment, the receiver 160 of the image decodingapparatus 150 may obtain the processing block size information from thebitstream according to each specific data unit. For example, theprocessing block size information may be obtained from the bitstream ina data unit such as an image, sequence, picture, slice, or slicesegment. That is, the receiver 160 may obtain the processing block sizeinformation from the bitstream according to each of the various dataunits, and the image decoding apparatus 150 may determine the size ofone or more processing blocks, which are split from the picture, byusing the obtained processing block size information. The size of theprocessing blocks may be integer times that of the reference codingunits.

According to an embodiment, the image decoding apparatus 150 maydetermine the size of processing blocks 1502 and 1512 included in thepicture 1500. For example, the image decoding apparatus 150 maydetermine the size of processing blocks based on the processing blocksize information obtained from the bitstream. Referring to FIG. 15,according to an embodiment, the image decoding apparatus 150 maydetermine a width of the processing blocks 1502 and 1512 to be fourtimes the width of the reference coding units, and may determine aheight of the processing blocks 1502 and 1512 to be four times theheight of the reference coding units. The image decoding apparatus 150may determine a determination order of one or more reference codingunits in one or more processing blocks.

According to an embodiment, the image decoding apparatus 150 maydetermine the processing blocks 1502 and 1512, which are included in thepicture 1500, based on the size of processing blocks, and may determinea determination order of one or more reference coding units in theprocessing blocks 1502 and 1512. According to an embodiment,determination of reference coding units may include determination of thesize of the reference coding units.

According to an embodiment, the image decoding apparatus 150 may obtain,from the bitstream, determination order information of one or morereference coding units included in one or more processing blocks, andmay determine a determination order with respect to one or morereference coding units based on the obtained determination orderinformation. The determination order information may be defined as anorder or direction for determining the reference coding units in theprocessing block. That is, the determination order of reference codingunits may be independently determined with respect to each processingblock.

According to an embodiment, the image decoding apparatus 150 may obtain,from the bitstream, the determination order information of referencecoding units according to each specific data unit. For example, thereceiver 160 may obtain the determination order information of referencecoding units from the bitstream according to each data unit such as animage, sequence, picture, slice, slice segment, or processing block.Because the determination order information of reference coding unitsindicates an order for determining reference coding units in aprocessing block, the determination order information may be obtainedwith respect to each specific data unit including an integer number ofprocessing blocks.

According to an embodiment, the image decoding apparatus 150 maydetermine one or more reference coding units based on the determineddetermination order.

According to an embodiment, the receiver 160 may obtain thedetermination order information of reference coding units from thebitstream as information related to the processing blocks 1502 and 1512,and the image decoding apparatus 150 may determine a determination orderof one or more reference coding units included in the processing blocks1502 and 1512 and determine one or more reference coding units, whichare included in the picture 1500, based on the determination order.Referring to FIG. 15, the image decoding apparatus 150 may determinedetermination orders 1504 and 1514 of one or more reference coding unitsin the processing blocks 1502 and 1512, respectively. For example, whenthe determination order information of reference coding units isobtained with respect to each processing block, different types of thedetermination order information of reference coding units may beobtained for the processing blocks 1502 and 1512. When the determinationorder 1504 of reference coding units in the processing block 1502 is araster scan order, reference coding units included in the processingblock 1502 may be determined according to a raster scan order. On thecontrary, when the determination order 1514 of reference coding units inthe other processing block 1512 is a backward raster scan order,reference coding units included in the processing block 1512 may bedetermined according to the backward raster scan order.

FIGS. 1 to 15 illustrate a method of splitting an image into a largestcoding unit, and splitting the largest coding unit into coding units ofa hierarchical tree structure. FIGS. 16 to 24 illustrate a method ofdetermining a quantization parameter of a current block.

The image encoding apparatus 100 of FIG. 1 may transform, through apreset procedure, residual data that is a difference between originalvalues of pixels included in a coding unit and prediction valuesthereof. In this regard, the image encoding apparatus 100 may reduce asize of the residual data, instead of losing the residual data byquantizing the transformed residual data.

The quantization of the residual data is performed based on aquantization parameter. The quantization parameter denotes an index usedto derive a scaling matrix necessary to quantize the residual data ofthe current block. When the quantization parameter is large, a scalingmatrix where elements are relatively large is derived. Therefore, whenthe quantization parameter is large, the residual data is lost in largequantities but a compression rate of the residual data is increased. Onthe contrary, when the quantization parameter is small, a scaling matrixwhere elements are relatively small is derived. Therefore, when thequantization parameter is small, the residual data is lost in smallquantities but a compression rate of the residual data is decreased.

That is, in a case where subjective image quality deterioration is smalleven when the compression rate of the residual data is increased, alarge quantization parameter may be used. However, in a case wheresubjective image quality deterioration is detected when the compressionrate of the residual data is increased, a small quantization parameterhas to be used. Therefore, different quantization parameters have to beused for blocks of a same picture, in consideration of deterioration inimage quality.

FIG. 16 illustrates an image decoding apparatus for determining aquantization parameter of a block and decoding residual data of theblock according to the determined quantization parameter.

An image decoding apparatus 1600 includes a quantization parameterdeterminer 1610 and an inverse-quantizer 1620. In FIG. 16, thequantization parameter determiner 1610 and the inverse-quantizer 1620are illustrated as separate components but, in another embodiment, thequantization parameter determiner 1610 and the inverse-quantizer 1620may be combined into one component.

In FIG. 16, the quantization parameter determiner 1610 and theinverse-quantizer 1620 are illustrated as being included in oneapparatus but devices performing respective functions of thequantization parameter determiner 1610 and the inverse-quantizer 1620may not be necessarily physically adjacent to each other. Therefore, inanother embodiment, the quantization parameter determiner 1610 and theinverse-quantizer 1620 may be dispersed.

The quantization parameter determiner 1610 and the inverse-quantizer1620 may be implemented by one processor according to an embodiment. Inanother embodiment, the quantization parameter determiner 1610 and theinverse-quantizer 1620 may be implemented by a plurality of processors.

The image decoding apparatus 1600 may perform inverse quantization basedon a quantization group including one or more blocks. Hereinafter, aninverse quantization method based on a quantization group will now bedescribed.

When a quantization parameter varies in each block, information aboutthe quantization parameter is increased. Therefore, when a quantizationparameter is determined with respect to a block unit, coding efficiencymay be decreased. Therefore, in order to increase coding efficiency, amethod of determining a same quantization parameter with respect to aplurality of blocks is being discussed.

In general, adjacent blocks have same or similar quantizationparameters. Therefore, the image decoding apparatus 1600 may use a samequantization parameter for adjacent blocks. A plurality of blocks thatare adjacent to each other and use a same quantization parameter arereferred to as a quantization group.

The quantization group may be determined based on a largest coding unit.For example, the quantization group may be set with respect to blockssplit from the largest coding unit by the preset number of times. When ablock for which a quantization group is set is not additionally split, aquantization parameter of the quantization group is applied to only theblock for which the quantization group is set. On the contrary, when theblock corresponding to the quantization group is additionally split, thequantization parameter of the quantization group may be applied to allsubblocks that are generated by splitting the block for which thequantization group is set.

Alternatively, the quantization group may be determined based on a size.For example, when a size of a block is equal to or smaller than aquantization group reference size, a quantization group may be set forthe block. When the block for which the quantization group is set is notadditionally split, a quantization parameter of the quantization groupis applied to only one block for which the quantization group is set. Onthe contrary, the block corresponding to the quantization group isadditionally split, the quantization parameter of the quantization groupmay be applied to all subblocks that are generated by splitting theblock for which the quantization group is set. Accordingly, aquantization parameter of blocks is determined based on a quantizationblock, such that information about the quantization parameter isdecreased.

The quantization parameter determiner 1610 may obtain a differencequantization parameter allowance flag with respect to an upper data unitof a current quantization group. When the difference quantizationparameter allowance flag indicates that it is allowed to determine aquantization parameter according to a difference quantization parameter,the quantization parameter determiner 1610 may obtain the differencequantization parameter of a current block.

The upper data unit may be one of a video parameter set (VPS), asequence parameter set (SPS), and a picture parameter set (PPS).Therefore, the quantization parameter determiner 1610 may apply a methodof determining a quantization parameter based on a quantization group toall blocks included in an upper data unit.

The quantization parameter determiner 1610 may obtain quantization groupinformation with respect to an upper data unit of a current quantizationgroup. The quantization group information indicates a method ofdetermining a quantization group. For example, the quantization groupinformation may include block split information or block sizeinformation. When the difference quantization parameter allowance flagallows a difference quantization parameter, the quantization parameterdeterminer 1610 may obtain the quantization group information.

The quantization parameter determiner 1610 may determine a predictedquantization parameter of the current quantization group, the predictedquantization parameter being determined according to at least one of theblock split information and the block size information.

The block split information may include the number of quadtree splittingtimes and the number of non-quadtree splitting times. The number ofquadtree splitting times indicates the number of times a quadtree splitis performed to obtain a current quantization group from a largestcoding block. For example, a split to blocks 210 d of FIG. 2 correspondsto a quadtree split.

The number of non-quadtree splitting times indicates the number of timesa split that is not the quadtree split is performed to obtain a currentquantization group from a largest coding block. For example, a splittingmethod shown in FIG. 3 corresponds to the non quadtree split.

The block size information may include an area of a block or a binarylogarithm (log) value of the area of the block. Also, a height and widthof the block or binary log values of the height and width of the blockmay be included therein.

According to an embodiment, the quantization parameter determiner 1610may determine the current quantization group according to the number ofquadtree splitting times. When only the quadtree split is used to splita largest coding unit, a quantization group may be set with respect to ablock having at least preset size according to the number of quadtreesplitting times. For example, when a size of the largest coding unit is256×256 and the number of quadtree splitting times is 2, thequantization group may be set for a block whose size is 64×64 or more.

FIGS. 17A to 17D are diagrams of embodiments in which a quantizationgroup is determined according to the number of quadtree splitting times.

Referring to FIG. 17A, a largest coding block 1700 is split into fourblocks 1702, 1704, 1706, and 1708 according to quadtree split. Thenumber of quadtree splitting times of the blocks 1702, 1704, 1706, and1708 is set to 1. The block 1704 is split into four blocks 1710, 1712,1714, and 1716 according to quadtree split. The number of quadtreesplitting times of the blocks 1710, 1712, 1714, and 1716 is set to 2.The block 1716 is split into four blocks 1718, 1720, 1722, and 1724according to quadtree split. The number of quadtree splitting times ofthe blocks 1718, 1720, 1722, and 1724 is set to 3. Based on the blocks1702, 1706, 1708, 1710, 1712, 1714, 1718, 1720, 1722, and 1724determined when a split of the largest coding block 1700 is completed,prediction and transformation encoding and decoding may be performed.

As shown in FIG. 17A, when the number of quadtree splitting times isincreased by 1, a size of a split block is decreased by a half.Therefore, only when quadtree split is allowed, a size of a block may bedetermined according to the number of quadtree splitting times.

FIG. 17B illustrates an embodiment in which a quantization group isdetermined with respect to a block for which the number of quadtreesplitting times is 1. Referring to FIG. 17B, quantization groups are setwith respect to four blocks 1702, 1704, 1706, and 1708 for which thenumber of quadtree splitting times is 1.

Each of the blocks 1702, 1706, and 1708 is solely included in each ofthe quantization groups for the blocks 1702, 1706, and 1708. However,the quantization group of the block 1704 includes subblocks 1710, 1712,1714, 1718, 1720, 1722, and 1724 of the block 1704. Therefore,quantization and inverse quantization according to a same quantizationparameter may be applied to the subblocks 1710, 1712, 1714, 1718, 1720,1722, and 1724 of the block 1704.

FIG. 17C illustrates an embodiment in which a quantization group isdetermined with respect to a block for which the number of quadtreesplitting times is 2. Referring to FIG. 17C, quantization groups are setwith respect to blocks 1702, 1706, 1708, 1710, 1712, 1714, and 1716 forwhich the number of quadtree splitting times is equal to or smaller than2. For the blocks 1702, 1706, and 1708, the number of quadtree splittingtimes is 1 but the blocks 1702, 1706, and 1708 are not additionallysplit, such that the quantization group is set with respect the blocks1702, 1706, and 1708.

Each of the blocks 1702, 1706, 1708, 1710, 1712, and 1714 is solelyincluded in each of the quantization groups therefor. However, thequantization group of the block 1716 includes subblocks 1718, 1720,1722, and 1724 of the block 1716. Therefore, quantization and inversequantization according to a same quantization parameter may be appliedto the subblocks 1718, 1720, 1722, and 1724 of the block 1716.

FIG. 17D illustrates an embodiment in which a quantization group isdetermined with respect to a block for which the number of quadtreesplitting times is 3. Because a block for which the number of quadtreesplitting times is 4 is not present in FIG. 17D, a quantization group isset with respect to all blocks 1702, 1706, 1708, 1710, 1712, 1714, 1718,1720, 1722, and 1724.

Referring to FIGS. 17A to 17D, when the number of quadtree splittingtimes of block split information is increased, a size of a quantizationgroup is decreased. On the contrary, when the number of quadtreesplitting times of the block split information is decreased, the size ofthe quantization group is increased. Therefore, a size of quantizationparameter information may be increased or decreased based on the numberof quadtree splitting times of block split information.

The quantization parameter determiner 1610 may determine a currentquantization group according to the number of quadtree splitting timesand the number of non-quadtree splitting times. When both quadtree splitand non quadtree split are applied to splitting of blocks, the method ofdetermining a quantization group shown in FIGS. 17A to 17D is not used.Therefore, a quantization group may be determined, in furtherconsideration of the number of non-quadtree splitting times, or a methodof determining a quantization group based on a size of the quantizationgroup may be applied thereto. FIGS. 18A to 18C illustrate an embodimentof a method of determining a quantization group in a largest codingblock to which non quadtree split is applied.

FIG. 18A illustrates how a largest coding block 1800 is split. A numbermarked in each block indicates the number of splitting times performedon the largest coding block 1800.

The largest coding block 1800 is quadtree split into four blocks 1802,1804, 1806, and 1808. Because the block 1802 is not additionally split,the number of splitting times of the block 1802 is 1. Hereinafter, it isassumed that a size of the largest coding block 1800 is 4N×4N.

The block 1804 is split into two 2N×N blocks 1810 and 1812. Then, theblock 1810 is split into two N×N blocks 1814 and 1816, and the block1812 is split into two N/2×N blocks 1818 and 1822 and one N×N block1820. The number of splitting times of subblocks 1814, 1816, 1818, 1820,1822 of the block 1804 is all 3.

The block 1806 is split into two N×2N blocks 1824 and 1826. Then, theblock 1824 is split into two N×N blocks 1828 and 1830, and the block1826 is split into two N×N/2 blocks 1840 and 1844 and one N×N block1842. The block 1828 is split into two N/2×N blocks 1832 and 1834. Theblock 1834 is split into two N/2×N/2 blocks 1836 and 1838. The number ofsplitting times of subblocks 1828, 1830, 1840, 1842, and 1844 of theblock 1806 is 3. The number of splitting times of the block 1832 splitfrom the block 1828 is 4, and the number of splitting times of theblocks 1836 and 1838 is 5.

The block 1808 is split into four N×N blocks 1846, 1848, 1850, and 1852.The block 1846 is split into four N×N blocks 1854, 1856, 1858, and 1860.Also, the block 1848 is split into two N×2N blocks 1862 and 1864, andthe block 1862 is split into two N×N blocks 1866 and 1868. The number ofsplitting times of the blocks 1850 and 1852 is 2, and the number ofsplitting times of the blocks 1854, 1856, 1858, 1860, and 1864 is 3. Thenumber of splitting times of the blocks 1866 and 1868 is 4.

When a quantization group is determined according to the number ofsplitting times of a block, a size of the quantization group may not beuniform. In detail, with reference to FIG. 18B, ununiformity in a sizeof a quantization group will now be described.

FIG. 18B illustrates an embodiment in which a quantization group is setwith respect to blocks whose number of splitting times is 3. Referringto FIG. 18B, a quantization group is set with respect to blocks 1802,1814, 1816, 1818, 1820, 1822, 1828, 1830, 1840, 1842, 1844, 1850, 1852,1854, 1856, 1858, 1860, 1862, and 1864 whose number of splitting timesis 3.

However, the number of splitting times of the block 1814 and the numberof splitting times of the block 1854 are equal, but a size of the block1814 is four times a size of the block 1854. Although a size of the 1836is equal to a size of the 1854, a quantization parameter of aquantization group corresponding to the block 1828 is applied whereas aquantization parameter of a quantization group corresponding to theblock 1854 is applied the block 1854.

Only when quadtree split is performed as in embodiments of FIGS. 17A to17D, sizes of quantization groups are same. However, as described above,in a case where quantization groups are set according to the number ofsplitting times when non-quadtree split is performed, sizes of thequantization groups are different.

FIG. 18C illustrates methods for solving the problem. For example, thequantization parameter determiner 1610 may determine a currentquantization group according to a weighted sum of the number of quadtreesplitting times and the number of non-quadtree splitting times. Quadtreesplit is the same as that vertical split and horizontal split aresequentially applied. Therefore, one quadtree split is substantially thesame as two non-quadtree splits.

Therefore, the quantization parameter determiner 1610 subdivides thenumber of splitting times into the number of quadtree splitting timesand the number of non-quadtree splitting times, and may set aquantization group based on a weighted sum of the number of quadtreesplitting times and the number of non-quadtree splitting times accordingto a weight of 2:1.

For example, the block 1814 is generated due to one quadtree split andtwo non-quadtree splits from a largest coding unit 1800. Therefore, aweighted sum of the number of quadtree splitting times and the number ofnon-quadtree splitting times according to a weight of 2:1 with respectto the block 1814 is 4. The block 1846 is generated due to two quadtreesplits from the largest coding unit 1800. Therefore, a weighted sum ofthe number of quadtree splitting times and the number of non-quadtreesplitting times according to a weight of 2:1 with respect to the block1846 is 4. Therefore, when a quantization group is set with respect to ablock whose weighted sum is 4, unlike FIG. 18B, in FIG. 18C, a block1854 obtains a quantization parameter from a quantization group set forthe block 1846.

According to another embodiment, the quantization parameter determiner1610 may determine a current quantization group based on a sum of aheight and a width of a block or an average of the height and the widthof the block. For example, when a quantization group is set with respectto a block with an N×N size, quantization groups are set with respect tothe block 1814 and the block 1846. Therefore, unlike FIG. 18B, in FIG.18C, the block 1854 obtains a quantization parameter from thequantization group set for the block 1846. Because upper blocks 1812 and1826 are larger than an N×N size and thus there is no quantization groupcorresponding thereto, even when blocks 1818, 1822, 1840, and 1844 aresmaller than the N×N size, quantization groups are set therefor.

Similarly, the quantization parameter determiner 1610 may determine acurrent quantization group based on a sum of binary log values of aheight and a width of a block or an average of binary log values of theheight and the width of the block. Alternatively, the quantizationparameter determiner 1610 may determine a current quantization groupbased on an area of a block or a binary log value of the area.

The quantization parameter determiner 1610 may determine a predictedquantization parameter of a current block, based on a quantizationparameter of an upper adjacent block of a current quantization group, aquantization parameter of a left adjacent block of the currentquantization group, and a quantization parameter of a quantization groupthat has been decoded just before the current quantization group.

For example, the quantization parameter determiner 1610 may determine,as a quantization parameter of the current quantization group, anaverage of the quantization parameter of the upper adjacent block andthe quantization parameter of the left adjacent block. When thequantization parameter of the upper adjacent block does not exist, thequantization parameter determiner 1610 may use, instead of thequantization parameter of the upper adjacent block, the quantizationparameter of the quantization group, which has been decoded just beforethe current quantization group, to determine the quantization parameterof the current quantization group. Equally, when the quantizationparameter of the left adjacent block does not exist, the quantizationparameter determiner 1610 may use, instead of the quantization parameterof the left adjacent block, the quantization parameter of thequantization group, which has been decoded just before the currentquantization group, to determine the quantization parameter of thecurrent quantization group.

Also, the quantization parameter determiner 1610 may determine a defaultquantization parameter of a slice or picture as a predicted quantizationparameter. For example, when the quantization parameter of the upperadjacent block, the quantization parameter of the left adjacent block,and the quantization parameter of the quantization group that has beendecoded just before the current quantization group, the currentquantization group refers to, do not exist, the default quantizationparameter may be used.

The quantization parameter determiner 1610 determines a differencequantization parameter of the current quantization group. Thequantization parameter determiner 1610 may obtain, from a bitstream,difference quantization parameter magnitude information and differencequantization parameter sign information. The quantization parameterdeterminer 1610 may determine the difference quantization parameter ofthe current quantization group, based on the difference quantizationparameter magnitude information and the difference quantizationparameter sign information.

When the current quantization group includes two or more blocks, thequantization parameter determiner 1610 may obtain the differencequantization parameter magnitude information and the differencequantization parameter sign information with respect to a block to befirst decoded in a scan order. Then, the quantization parameterdeterminer 1610 does not obtain the difference quantization parametermagnitude information and the difference quantization parameter signinformation with respect to remaining blocks of the current quantizationgroup, and applies a quantization parameter to the remaining blocks, thequantization parameter being determined with respect to the block to befirst decoded. Therefore, as a result, the quantization parameterdeterminer 1610 applies the same quantization parameter to all blocks ofthe current quantization group.

When the quantization parameter determiner 1610 decodes all blocks ofthe current quantization group, and then decodes a block of a newquantization group, the quantization parameter determiner 1610 mayinitialize a difference quantization parameter and differencequantization parameter-related information. The difference quantizationparameter-related information may include difference quantizationparameter decoding information indicating whether the differencequantization parameter has been already decoded, and quantization groupposition information indicating a position of a quantization group.

The quantization parameter determiner 1610 may initialize the differencequantization parameter and the difference quantization parameter-relatedinformation, and may obtain new difference quantization parametermagnitude information and new difference quantization parameter signinformation from a bitstream.

The quantization parameter determiner 1610 determines a quantizationparameter of the current quantization group, based on the predictedquantization parameter and the difference quantization parameter of thecurrent quantization group. In detail, the quantization parameterdeterminer 1610 may determine the quantization parameter, based on a sumof the predicted quantization parameter and the difference quantizationparameter of the current quantization group. According to an embodiment,the quantization parameter determiner 1610 may obtain quantizationparameter offset information from a bitstream, and may adjust thedetermined quantization parameter according to the quantizationparameter offset information.

The inverse-quantizer 1620 inverse quantizes the current block includedin the current quantization group, based on the quantization parameterof the current quantization group.

FIG. 19 illustrates a syntax structure about a method of decoding adifference quantization parameter included in a bitstream when quadtreesplit and non-quadtree split are all allowed.

Table in the top of FIG. 19 shows quadtree split syntax structure(coding_quadtree). The quadtree split syntax structure of FIG. 19provides a configuration of determining whether to initialize adifference quantization parameter and difference quantizationparameter-related information before whether to perform quadtree splitis determined.

In the quadtree split syntax structure of FIG. 19,“cu_qp_delta_enabled_flag” indicates a difference quantizationparameter-enabled flag, “cqtDepth” indicates the number of quadtreesplitting times, and “diff_cu_qp_delta_depth” indicates block splitinformation. “CuQpDeltaVal” indicates a difference quantizationparameter, “IsCuQpDeltaCoded” indicates difference quantizationparameter decoding information, and “CuQgTopLeftX” and “CuQgTopLeftY”indicate quantization group position information.

Referring to FIG. 19, when “cu_qp_delta_enabled_flag” indicates 1 and“cqtDepth” is equal to or smaller than “diff_cu_qp_delta_depth”,“CuQpDeltaVal” and “IsCuQpDeltaCoded” are determined to be 0, and“CuQgTopLeftX” and “CuQgTopLeftY” are determined as x0 and y0 thatindicate an upper-left sample position of a current block.

When “cu_qp_delta_enabled_flag” indicates 1, this means that it isallowed to obtain a difference quantization parameter.

When “cqtDepth” is equal to or smaller than “diff_cu_qp_delta_depth”,this means that the number of quadtree splitting times of the currentblock is equal to or smaller than the number of splitting times that isa reference of a quantization group indicated by the block splitinformation. The feature that the number of quadtree splitting times ofthe current block is equal to or smaller than the number of splittingtimes that is the reference of the quantization group means that thecurrent block is not included in a quantization group of a block decodedbefore the current block.

When the above conditions are satisfied, “CuQpDeltaVal” and“IsCuQpDeltaCoded” are determined to be 0, and a new differencequantization parameter about a quantization group positioned at“CuQgTopLeftX” and “CuQgTopLeftY” is obtained based on differencequantization parameter information that is newly obtained from abitstream.

Table in the middle of FIG. 19 shows non-quadtree split syntaxstructure. The non-quadtree split syntax structure of FIG. 19 provides aconfiguration of determining whether to initialize a differencequantization parameter and difference quantization parameter-relatedinformation before whether to perform non-quadtree split is determined.

In the non-quadtree split syntax structure of FIG. 19,“cu_qp_delta_enabled_flag” indicates a difference quantizationparameter-enabled flag, “cqtDepth” indicates the number of quadtreesplitting times, “mttDepth” indicates the number of non-quadtreesplitting times, and “diff_cu_qp_delta_depth” indicates block splitinformation. “CuQpDeltaVal” indicates a difference quantizationparameter, “IsCuQpDeltaCoded” indicates difference quantizationparameter decoding information, and “CuQgTopLeftX” and “CuQgTopLeftY”indicate quantization group position information.

Referring to FIG. 19, when “cu_qp_delta_enabled_flag” indicates 1 and asum of “cqtDepth” and “mttDepth” is equal to or smaller than“diff_cu_qp_delta_depth”, “CuQpDeltaVal” and “IsCuQpDeltaCoded” aredetermined to be 0, and “CuQgTopLeftX” and “CuQgTopLeftY” are determinedas x0 and y0 that indicate an upper-left sample position of a currentblock.

Similar to the quadtree split syntax structure, even in the non-quadtreesplit syntax structure, a difference quantization parameter anddifference quantization parameter-related information are initialized.However, unlike the quadtree split syntax structure, in the non-quadtreesplit syntax structure, the sum of “cqtDepth” and “mttDepth”, instead of“cqtDepth”, is compared with “diff_cu_qp_delta_depth”. In FIG. 19, thesum of “cqtDepth” and “mttDepth” is compared with“diff_cu_qp_delta_depth”, but, according to an embodiment, a weightedsum of “cqtDepth” and “mttDepth” may be compared with“diff_cu_qp_delta_depth”.

Table in the bottom of FIG. 19 shows transform block syntax structure.tu_cbf_luma[x0][y0] indicates whether a current luma block positioned at(x0, y0) has residual data. Then, tu_cbf_cb[x0][y0] andtu_cbf_cr[x0][y0] indicate whether a current Cb block and a current Crblock respectively positioned at (x0, y0) have residual data. When thecurrent luma block, the current Cb block, and the current Cr block donot have residual data, difference quantization parameter information isnot obtained.

On the contrary, when at least one of the current luma block, thecurrent Cb block, and the current Cr block includes residual data,“cu_qp_delta_abs” indicating difference quantization parameter magnitudeinformation and “cu_qp_delta_sign_flag” indicating differencequantization parameter sign information are obtained from a bitstream.Then, “CuQpDeltaVal” indicating a difference quantization parameter isdetermined from “cu_qp_delta_abs” and “cu_qp_delta_sign_flag”. Also,“IsCuQpDeltaCoded” indicating whether a difference quantizationparameter exists is determined as 1.

When a block to be decoded after the current block is included in a samequantization group of the current block (i.e., when “cqtDepth” or a(weighted) sum of “cqtDepth” and “mttDepth” is greater than“diff_cu_qp_delta_depth”), “CuQpDeltaVal” and “IsCuQpDeltaCoded” are notinitialized, and thus, the block to be decoded after the current blockis inverse quantized according to “CuQpDeltaVal” used in a decodingprocedure with respect to the current block.

In FIG. 19, a configuration of obtaining difference quantizationparameter information is implemented in the transform block syntaxstructure, but, according to an embodiment, the configuration may beimplemented in other syntax.

FIG. 20 illustrates an image decoding method of determining aquantization parameter of a block according to a quantization group, anddecoding residual data of a block according to the determinedquantization parameter.

In operation 2010, a predicted quantization parameter of a currentquantization group determined according to at least one of block splitinformation and block size information is determined.

The current quantization group may be determined according to the numberof quadtree splitting times and the number of non-quadtree splittingtimes. In detail, the current quantization group may be determinedaccording to a weighted sum of the number of quadtree splitting timesand the number of non-quadtree splitting times.

The current quantization group may be determined based on a sum of aheight and a width of a block or an average of the height and the widthof the block. Alternatively, the current quantization group may bedetermined based on a sum of binary log values of a height and a widthof a block or an average of binary log values of the height and thewidth of the block. Alternatively, the current quantization group may bedetermined based on an area of a block or a binary log value of thearea.

The predicted quantization parameter of a current block may bedetermined based on a quantization parameter of an upper adjacent blockof a current quantization group, a quantization parameter of a leftadjacent block of the current quantization group, and a quantizationparameter of a quantization group that has been decoded immediatelybefore the current quantization group.

In operation 2020, a difference quantization parameter of the currentquantization group is determined. In detail, difference quantizationparameter magnitude information and difference quantization parametersign information may be obtained from a bitstream. Then, the differencequantization parameter of the current quantization group may bedetermined based on the difference quantization parameter magnitudeinformation and the difference quantization parameter sign information.

According to an embodiment, when a difference quantizationparameter-enabled flag indicates that it is allowed to determine aquantization parameter according to the difference quantizationparameter, a difference quantization parameter of the current block maybe obtained.

In operation 2030, a quantization parameter of the current quantizationgroup is determined based on the predicted quantization parameter andthe difference quantization parameter of the current quantization group.For example, the quantization parameter of the current quantizationgroup is determined may be determined based on a sum of the predictedquantization parameter and the difference quantization parameter.

In operation 2040, the current block included in the currentquantization group is inverse quantized according to the quantizationparameter of the current quantization group.

The image decoding method of FIG. 20 may include various embodimentsabout a method of determining a quantization parameter according to aquantization group of the image decoding apparatus of FIG. 16.

The image decoding apparatus 1600 may perform inverse quantization basedon a quantization parameter unit indicating an area where a samequantization parameter is used. Hereinafter, an inverse quantizationmethod based on a quantization parameter unit will now be described.

FIG. 21 illustrates an embodiment of a quantization parameter unitstructure and a coding block tree structure.

A picture or slice may differ in subjective image quality deteriorationin their parts Therefore, for optimization of coding efficiency, it isnecessary to set different quantization parameters according tocharacteristics of respective parts of the picture or the slice. Adistribution of quantization parameters is not equal to a coding blocktree structure that is a basic unit of coding. Therefore, a quantizationparameter unit map is determined independently from the coding blocktree structure.

In FIG. 21, a quantization parameter unit 2110 may be a rectangle of anM×N size. Here, a picture is represented as a quantization parameter map2120 composed of a plurality of quantization parameter units. Each ofthe quantization parameter units in the quantization parameter map 2120has a quantization parameter. In FIG. 21, the quantization parameterunit 2110 is illustrated as a rectangle, but, according to anembodiment, the quantization parameter unit 2110 may be illustrated asan irregular shape not the rectangle.

A quantization parameter of the quantization parameter unit 2110 may bedetermined according to a characteristic of a part of a correspondingpicture. The quantization parameter map 2120 and the quantizationparameter of the quantization parameter unit 2110 are encoded anddecoded independently from prediction coding information according to acoding block structure 2140. When residual data of a coding block 2130is encoded and decoded, a quantization parameter may be obtained fromthe quantization parameter unit 2110 which corresponds to a position ofthe coding block 2130.

The quantization parameter determiner 1610 may match a current block toa current quantization parameter unit, based on at least one of aposition and a size of the current block.

For example, the quantization parameter determiner 1610 may determine,as the current quantization parameter unit of the current block, aquantization parameter unit including coordinate values of an upper-leftsample of the current block.

As another example, when the current block includes a plurality ofquantization parameter units, the quantization parameter determiner 1610may determine the plurality of quantization parameter units as currentquantization parameter units of the current block. In this regard, thequantization parameter determiner 1610 may determine, as a quantizationparameter of the current block, an average value of a plurality ofquantization parameters of the current quantization parameter units.

FIGS. 22A and 22B illustrate a method of determining a quantizationparameter unit corresponding to a current block.

FIG. 22A illustrates an embodiment in which a quantization parameterunit 2200 corresponds to a plurality of coding blocks 2202 to 2224.Blocks 2202, 2204, 2206, 2210, 2212, and 2214 that are all included inthe quantization parameter unit 2200 are inverse quantized according toa quantization parameter corresponding to the quantization parameterunit 2200.

Then, blocks whose parts are included in the quantization parameter unit2200 may be determined with respect to whether a quantization parameterof the quantization parameter unit 2200 is to be applied thereto, basedon an upper-left sample of a block. Therefore, blocks 2208, 2216, 2218,2220, 2222, and 2224 whose upper-left samples are included in thequantization parameter unit 2200 may be inverse quantized according tothe quantization parameter corresponding to the quantization parameterunit 2200.

In FIG. 22A, an embodiment in which a quantization parameter unit isdetermined based on an upper-left sample of a block is described, but,according to an embodiment, a quantization parameter unit of a block maybe determined based on a center sample, an upper-right sample, alower-left sample, a lower-right sample, or the like of the block.

FIG. 22B illustrates an embodiment in which a plurality of quantizationparameter units 2252 to 2274 correspond to a block 2250.

The quantization parameter units 2252, 2254, 2258, 2260, 2264, and 2266are entirely included in the block 2250. Therefore, the block 2250 maybe inverse quantized according to at least one quantization parameterfrom among the quantization parameter units 2252, 2254, 2258, 2260,2264, and 2266. For example, a quantization parameter of the block 2250may be determined to be an average of quantization parameters of thequantization parameter units 2252, 2254, 2258, 2260, 2264, and 2266.

Alternatively, the quantization parameter units 2256, 2262, 2268, 2270,2272, and 2274 that partly overlap with the block 2250 may be used todetermine the quantization parameter of the block 2250. Therefore, theblock 2250 may be inverse quantized according to a quantizationparameter determined according to at least one of the quantizationparameter units 2252 to 2274.

FIGS. 23A and 23B illustrate a correlation between a block and aquantization parameter unit.

FIG. 23A illustrates a block tree structure and a quantization parametermap, according to an embodiment. According to an embodiment, aquantization parameter unit corresponding to an upper-left sample of ablock corresponds to the block. Therefore, a block 2308 corresponds to aquantization parameter unit 2300, a block 2310 corresponds to aquantization parameter unit 2302, a block 2312 corresponds to aquantization parameter unit 2304, and a block 2314 corresponds to aquantization parameter unit 2306. When correspondence references of ablock and a quantization parameter unit are different, otherquantization parameter units 2302, 2304, and 2306 may correspond to theblock 2308.

FIG. 23B illustrates a block tree structure and a quantization parametermap, according to an embodiment. As in FIG. 23A, when a quantizationparameter unit corresponding to an upper-left sample of a blockcorresponds to the block, all of blocks 2328, 2330, 2332, and 2334correspond to a quantization parameter unit 2334. Because a quantizationparameter of the quantization parameter unit 2334 is applied to all ofthe blocks 2328, 2330, 2332, and 2334, a quantization parameter is firstcalculated with respect to the block 2328 having an earliest decodingorder. Then, the quantization parameter used for the block 2328 may bechangelessly used for the blocks 2330, 2332, and 2334.

A quantization parameter is not determined for a block that does nothave residual data. For example, when the block 2328 does not haveresidual data, inverse-quantization is not necessary for the block 2328,and thus, a quantization parameter of the block 2328 is not determined.When the block 2330 to be decoded after the block 2328 has residualdata, a quantization parameter of the block 2330 may be determined.Then, the quantization parameter used for the block 2330 may bechangelessly used for the blocks 2332 and 2334.

The quantization parameter determiner 1610 may obtain a predictedquantization parameter with respect to a current quantization parameterunit.

The quantization parameter determiner 1610 may obtain the predictedquantization parameter from at least one of a left quantizationparameter unit of the current quantization parameter unit, an upperquantization parameter unit of the current quantization parameter unit,and a block decoded immediately before a current block.

Alternatively, the quantization parameter determiner 1610 may determine,as the predicted quantization parameter with respect to the currentquantization parameter unit, a predicted quantization parameter withrespect to a picture or slice including the current quantizationparameter unit.

The quantization parameter determiner 1610 may obtain a differencequantization parameter with respect to the current quantizationparameter unit.

The quantization parameter determiner 1610 may determine a quantizationparameter of the current quantization parameter unit, based on thepredicted quantization parameter and the difference quantizationparameter.

The inverse-quantizer 1620 may inverse quantize the current blockaccording to the quantization parameter of the current quantizationparameter unit.

FIG. 24 illustrates an image decoding method of determining aquantization parameter of a block according to a quantization parameterunit, and decoding residual data of the block according to thedetermined quantization parameter.

In operation 2410, a current block is matched to a current quantizationparameter unit, based on at least one of a position and a size of thecurrent block.

According to an embodiment, a quantization parameter unit includingcoordinate values of an upper-left sample of the current block may bedetermined as the current quantization parameter unit of the currentblock.

According to an embodiment, when the current block includes a pluralityof quantization parameter units, the plurality of quantization parameterunits may be determined as the current quantization parameter unit ofthe current block. In this regard, a current quantization parameter ofthe current block may be determined from at least one of the pluralityof quantization parameter units.

In operation 2420, a predicted quantization parameter with respect tothe current quantization parameter unit is obtained.

According to an embodiment, the predicted quantization parameter may beobtained from at least one of a left quantization parameter unit of thecurrent quantization parameter unit, an upper quantization parameterunit of the current quantization parameter unit, and a block decodedimmediately before the current block.

Alternatively, a predicted quantization parameter with respect to apicture or slice including the current quantization parameter unit maybe determined as the predicted quantization parameter with respect tothe current quantization parameter unit.

In operation 2430, a difference quantization parameter with respect tothe current quantization parameter unit is obtained.

In operation 2440, a quantization parameter of the current quantizationparameter unit is determined based on the predicted quantizationparameter and the difference quantization parameter.

In operation 2450, the current block is inverse quantized according tothe quantization parameter of the current quantization parameter unit.

The image decoding method of FIG. 24 may include various embodimentsabout a method of determining a quantization parameter according to aquantization group of the image decoding apparatus of FIG. 16.

Spatial-domain image data may be encoded for each of coding units of atree structure by an image encoding technique based on the coding unitsof the tree structure and may be reconstructed by decoding each oflargest coding units by an image decoding technique based on codingunits of a tree structure as described above with reference to FIGS. 1to 24, such that a picture and an image which is a picture sequence maybe reconstructed. The reconstructed video may be reproduced by areproducing device, may be stored in a storage medium, or may betransmitted via a network.

The above-described embodiments of the disclosure may be embodied as acomputer executable program and implemented via a computer-readablerecording medium by a general-purpose digital computer for execution ofthe program.

While the disclosure has been described above in connection withspecific best embodiments, other disclosures derivable by makingalternatives, modifications, and changes in the disclosure will beapparent to one of ordinary skill in the art, in view of theaforementioned descriptions. That is, the appended claims should beunderstood to cover all such alternatives, modifications and changes.Therefore, all the matters described in the present specification andillustrated in the drawings should be interpreted in an illustrative andnon-limiting sense.

1. An image decoding method comprising: splitting an upper coding blockinto a plurality of lower coding blocks according to split information;determining a current quantization group based on a split value of acurrent coding block among the plurality of lower coding blocks and asplit value of the current quantization group; obtaining a quantizationparameter of the current quantization group based on a predictedquantization parameter and a difference quantization parameter; andinverse-quantizing transform coefficients in a current transform blockin the current coding block using the quantization parameter, whereinthe difference quantization parameter is obtained using informationregarding an absolute value of the difference quantization parameter andinformation regarding a sign of the difference quantization parameter,and wherein: the split value of the current coding block is increased by1 if the current coding block is obtained by splitting the upper codingblock into two lower coding blocks according to non-quadtree split, andthe split value of the current coding block is increased by 2 if thecurrent coding block is obtained by splitting the upper coding blockinto four lower coding blocks according to quadtree split.
 2. An imagedecoding apparatus comprising: at least one processor configured to:split an upper coding block into a plurality of lower coding blocksaccording to split information; determine a current quantization groupbased on a split value of a current coding block among the plurality oflower coding blocks and a split value of the current quantization group;obtain a quantization parameter of the current quantization group basedon a predicted quantization parameter and a difference quantizationparameter; and inverse-quantize transform coefficients in a currenttransform block in the current coding block using the quantizationparameter, wherein the difference quantization parameter is obtainedusing information regarding an absolute value of the differencequantization parameter and information regarding a sign of thedifference quantization parameter, and wherein: the split value of thecurrent coding block is increased by 1 if the current coding block isobtained by splitting the upper coding block into two lower codingblocks according to non-quadtree split, and the split value of thecurrent coding block is increased by 2 if the current coding block isobtained by splitting the upper coding block into four lower codingblocks according to quadtree split.
 3. An image encoding methodcomprising: splitting an upper coding block into a plurality of lowercoding blocks; determining a current quantization group based on a splitvalue of a current coding block among the plurality of lower codingblocks and a split value of the current quantization group; obtaining aquantization parameter of the current quantization group; and quantizingcoefficients in a current transform block in the current coding blockusing the quantization parameter, wherein a difference quantizationparameter is obtained based on the quantization parameter of the currentquantization group and a predicted quantization parameter, whereininformation regarding an absolute value of the difference quantizationparameter and information regarding a sign of the differencequantization parameter are obtained using the difference quantizationparameter, and wherein: the split value of the current coding block isincreased by 1 if the current coding block is obtained by splitting theupper coding block into two lower coding blocks according tonon-quadtree split, and the split value of the current coding block isincreased by 2 if the current coding block is obtained by splitting theupper coding block into four lower coding blocks according to quadtreesplit.